Implantable head located radiofrequency coupled neurostimulation system for head pain

ABSTRACT

A system is provided for driving an implantable neurostimulator lead, the lead having an associated plurality of electrodes disposed in at least one array on the lead. The system comprises an implantable pulse generator (IPG), the IPG including an electrode driver, a load system for determining load requirements, an IPG power coupler, and an IPG communication system. The system also includes an external unit, which includes an external variable power generator, an external power coupler, an external communication system, and a controller for varying the power level of the variable power generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/989,674, filed Jan. 6, 2016, entitled IMPLANTABLE HEAD LOCATEDRADIOFREQUENCY COUPLED NEUROSTIMULATION SYSTEM FOR HEAD PAIN, thespecification of which is incorporated by reference herein in itsentirety. U.S. patent application Ser. No. 14/989,674 is aContinuation-in-Part of U.S. patent application Ser. No. 14/879,943,filed Oct. 9, 2015, entitled SURGICAL METHOD FOR IMPLANTABLE HEADMOUNTED NEUROSTIMULATION SYSTEM FOR HEAD PAIN, the specification ofwhich is incorporated by reference herein in its entirety. U.S. patentapplication Ser. No. 14/879,943 is a Continuation-in-Part of U.S. patentapplication Ser. No. 14/717,912, filed May 20, 2015, entitledIMPLANTABLE HEAD MOUNTED NEUROSTIMULATION SYSTEM FOR HEAD PAIN, thespecification of which is incorporated by reference herein in itsentirety. U.S. patent application Ser. No. 14/717,912 is a Continuationof U.S. patent application Ser. No. 14/460,139, filed Aug. 14, 2014,entitled IMPLANTABLE HEAD MOUNTED NEUROSTIMULATION SYSTEM FOR HEAD PAIN,now issued as U.S. Pat. No. 9,042,991, the specification of which isincorporated by reference herein in its entirety. U.S. patentapplication Ser. No. 14/460,139 claims benefit of U.S. ProvisionalApplication No. 61/894,795, filed Oct. 23, 2013, entitled IMPLANTABLEHEAD MOUNTED NEUROSTIMULATION SYSTEM FOR HEAD PAIN, the specification ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to implantable neurostimulation systemsand methods of treating migraine headaches and other forms of chronichead pain.

BACKGROUND OF THE INVENTION

Neurostimulation systems comprising implantable neurostimulation leadsare used to treat chronic pain. Conventional implantable peripheralneurostimulation leads are designed for placement in the spinal canal aspart of a spinal cord stimulation system, and for the therapeuticpurpose of treating various forms of chronic back and extremity pain.Implantable neurostimulation systems may either be powered by aninternal battery or by an external power source coupled to the internalunit by a radiofrequency interface.

SUMMARY OF THE INVENTION

In various implementations, an implantable head-mounted,radiofrequency-coupled, unibody peripheral nerve stimulation system maybe configured for implantation of substantially all electronics, exceptfor an on-site battery, at or near the implanted electrodes on theskull. The system may include an implantable pulse generator (IPG) fromwhich two neurostimulating leads may extend to a length sufficient toprovide therapeutic neurostimulation unilaterally over the frontal,parietal and occipital regions of the hemicranium. The IPG may have acomponent, or extension, containing an internal radiofrequency receiver,the purpose of which is to couple to an external power source andcontrol unit. The system may be operable to provide medically acceptabletherapeutic neurostimulation to multiple regions of the head, includingthe frontal, parietal and occipital regions of the hemicraniumsubstantially simultaneously.

Each of the leads may include an extended lead body; a plurality ofsurface metal electrodes disposed along the lead body, which may bedivided into two or more electrode arrays; and a plurality of internalelectrically conducting metal wires running along at least a portion ofthe length of the lead body and individually connecting an internalcircuit of the IPG to individual surface metal electrodes. The extendedlead body may comprise a medical grade plastic.

Implementations may include one or more of the following features. TheIPG may be of proper aspect ratio with respect to the specific site ofintended implantation in the head, such as an area posterior to and/orsuperior to the ear. The IPG may include an antenna coil and anapplication specific integrated circuit (ASIC). The IPG may beconfigured for functionally connecting with an external radiofrequencyunit.

Implementations may include one or more of the following features. Aneurostimulating lead may not include a central channel for a stylet. Aneurostimulating lead may have a smaller diameter than conventionalleads.

Implementations may include one or more of the following features. Thesystem may include the disposition of a sufficient plurality of surfaceelectrodes over a sufficient linear distance along the neurostimulatingleads to enable medically adequate therapeutic stimulation acrossmultiple regions of the head, including the frontal, parietal, andoccipital region of the hemicranium substantially simultaneously. Theextended array of surface electrodes may be divided into two or morediscrete terminal surface electrode arrays. The linear layout of themultiple surface electrode arrays may include at least one arraypositioned over the frontal region, at least one array positioned overthe parietal region, and at least one array positioned over theoccipital region. Specific intra-array design features may includevariations in the specific number of electrodes allotted to each group;the shape of the electrodes, e.g., whether the electrodes arecylindrical or flattened; the width of each electrode within each array,and the linear distance intervals of separation of the electrodes withineach array.

Various implementations may include a plurality of connection ports thatcan be connected with a plurality of leads and thus allow for attachingadditional leads.

The external radiofrequency unit may be operable to perform variousfunctions including recharging the rechargeable battery, diagnosticallyevaluating the IPG, and programming the IPG.

In various implementations, methods of treating chronic pain may includemethods of treating chronic head and/or face pain pain of multipleetiologies, including migraine headaches; and other primary headaches,including cluster headaches, hemicrania continua headaches, tension typeheadaches, chronic daily headaches, transformed migraine headaches;further including secondary headaches, such as cervicogenic headachesand other secondary musculokeletal headaches.

In various implementations, methods of treating chronic pain may includemethods of treating head and/or face pain of multiple etiologies,including neuropathic head and/or face pain, nociceptive head and/orface pain, and/or sympathetic related head and/or face pain.

In various implementations, methods of treating chronic pain may includemethods of treating head and/or face pain of multiple etiologies,including greater occipital neuralgia, as well as the other variousoccipital neuralgias, supraorbital neuralgia, auroiculotemporalneuralgia, infraorbital neuralgia, and other trigeminal neuralgias, andother head and face neuralgias.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features,objects, and advantages of the implementations will be apparent from thedescription and drawings.

In certain aspects, a method is provided for controlling power deliveryfrom an external power transfer system (EPTS) to at least oneimplantable neurostimulation system (INS). In some embodiments, themethod includes driving a first transmit coil within the EPTS with aresonant current having a peak magnitude, using a transmit coil drivercircuit within the EPTS. The method also includes receiving, using areceive coil within a first INS tuned to the resonant frequency of thefirst transmit coil, power transferred from the first transmit coil, andcoupling the received power to a regulator circuit within the first INSwhich is configured to provide an electrode current to an electrodedriver circuit within the first INS for a plurality of electrodestherewithin. The method further includes monitoring the regulatorcircuit within the first INS to determine whether the received powercoupled thereto is sufficient to achieve current regulation of theregulator circuit within the first INS. The method further includescommunicating a message to the EPTS using a back telemetry transmitcircuit within the first INS, the message requesting a change in powertransfer from the EPTS based upon the regulator circuit determination,and receiving, using a back telemetry receive circuit within the EPTS,the message communicated by the first INS. The method also includesadjusting the transmit coil driver circuit within the EPTS to change thepeak magnitude of the resonant current, corresponding to the requestedchange in power transfer.

In some embodiments, the method also includes a message which includes arequest to increase power transfer from the EPTS if the regulatorcircuit within the first INS is not achieving current regulation, andincludes a corresponding change in the peak magnitude of the resonantcurrent which includes an increase in peak magnitude. Some embodimentswill additionally include adjusting the transmit coil driver circuitwithin the EPTS to decrease the peak magnitude of the resonant current,if no message requesting an increase in power transfer from the EPTS hasbeen received from the first INS for at least a certain period of time.

In some embodiments, the message includes a request to decrease powertransfer from the EPTS if the regulator circuit within the first INS isachieving current regulation, and the corresponding change in the peakmagnitude of the resonant current includes a decrease in the peakmagnitude.

In some embodiments, the monitoring the regulator circuit within thefirst INS is performed under control of a state machine circuit withinthe first INS, and the communicating a first message to the EPTS isperformed under control of an instruction-based processor within thefirst INS. In some embodiments, the state machine circuit within thefirst INS is configured to wake-up the instruction-based processorwithin the first INS, in the event the instruction-based processor isnot already awake, to communicate the first message.

In some embodiments, monitoring the regulator circuit within the firstINS includes comparing the electrode current provided by the regulatorcircuit within the first INS against a prescribed electrode current forthe electrode driver circuit within the first INS corresponding to astimulation configuration programmed therein, and determining that theregulator circuit is achieving current regulation if the electrodecurrent is greater than or equal to the prescribed electrode current. Insome embodiments, comparing the electrode current against the prescribedelectrode current is performed under control of a state machine circuitwithin the first INS.

In some embodiments, coupling the received power to a regulator circuitwithin the first INS includes rectifying a current induced on thereceive coil, to generate a rectified voltage on an input node of theregulator circuit within the first INS. In some embodiments, monitoringthe regulator circuit within the first INS includes monitoring an inputvoltage and an output voltage of the regulator circuit within the firstINS, and determining that the regulator circuit is achieving currentregulation if a voltage differential between the input voltage and theoutput voltage exceeds a predetermined value.

In some embodiments, the method further includes de-tuning the receivecoil within the first INS, using a de-tuning circuit within the firstINS, to substantially inhibit power transfer from the EPTS to the firstINS.

In some embodiments, the regulator circuit within the first INS isfurther configured to provide a charging current to a charge storagedevice within the first INS. In certain of these embodiments, monitoringthe regulator circuit within the first INS includes comparing theelectrode current provided by the regulator circuit within the first INSagainst a prescribed electrode current for the electrode driver circuitwithin the first INS corresponding to a stimulation configurationprogrammed therein, comparing the charging current provided by theregulator circuit within the first INS against a predetermined chargingcurrent, and determining that the regulator circuit is achieving currentregulation if the electrode current is greater than or equal to theprescribed electrode current, and the charging current is greater thanor equal to the predetermined charging current. In certain of theseembodiments, the charge storage device is a supercapacitor.

In some embodiments, the method further includes driving, using thetransmit coil driver circuit within the EPTS, the resonant currentthrough a second transmit coil coupled in series with the first transmitcoil within the EPTS; receiving, using a receive coil within a secondINS tuned to the resonant frequency of the second transmit coil, powertransferred from the second transmit coil; coupling the received powerwithin the second INS to a regulator circuit within the second INS whichis configured to provide an electrode current to an electrode drivercircuit within the second INS for a plurality of electrodes therewithin;monitoring the regulator circuit within the second INS to determinewhether the received power coupled thereto is sufficient to achievecurrent regulation of the regulator circuit within the second INS;communicating a message from the second INS to the EPTS using a backtelemetry transmit circuit within the second INS, said messagerequesting a change in power transfer from the EPTS based upon saidregulator circuit determination for the second INS; receiving, using theback telemetry receive circuit within the EPTS, the third messagecommunicated by the second INS; and adjusting the transmit coil drivercircuit within the EPTS to change the peak magnitude of the resonantcurrent, corresponding to the requested change in power transferconveyed in the message communicated by the second INS.

In some embodiments, the method further includes adjusting the transmitcoil driver circuit within the EPTS to decrease the peak magnitude ofthe resonant current, if no message requesting an increase in powertransfer from the EPTS has been received from the first INS, and nomessage requesting an increase in power transfer from the EPTS has beenreceived from the second INS, for at least a certain period of time.

In some embodiments, the method further includes de-tuning the receivecoil within the second INS, using a de-tuning circuit within the secondINS, to substantially inhibit power transfer from the EPTS to the secondINS without inhibiting power transfer from the EPTS to the first INS.

In some embodiments, the first and second INSs are head-located beneatha dermis layer, or skin, of a patient.

In another embodiment, a system is provided for controlling powerdelivery from an external power transfer system (EPTS) to at least oneimplantable neurostimulation system (INS). In some embodiments thesystem includes an EPTS disposed outside a body, and at least one INSdisposed beneath a dermis layer of the body. The EPTS includes a groupof one or more transmit coils disposed in series, each corresponding toa respective INS; a transmit coil driver circuit operable to drive thegroup of one or more transmit coils with a resonant current having apeak magnitude; and a back telemetry circuit operable to receive amessage communicated by an INS. Each of said at least one INSrespectively includes a receive coil tuned to the resonant frequency ofthe corresponding transmit coil and operable to receive powertransferred therefrom when in proximity thereto; a regulator circuithaving an input to which the received power is coupled, and operable toprovide on an output thereof an electrode current to an electrode drivercircuit for a plurality of electrodes; a monitoring circuit operable todetermine whether the received power is sufficient to achieve currentregulation of the regulator circuit; and a back telemetry circuitoperable to communicate a message to the EPTS. Each respective INS isoperable to communicate a respective message requesting a change inpower transfer from the EPTS based upon the respective regulator circuitdetermination; and the EPTS is operable to adjust the transmit coildriver circuit to change the peak magnitude of the resonant current,based upon respective messages from one or more respective INS.

In some embodiments, each respective message includes a request toincrease power transfer from the EPTS if the respective regulatorcircuit is not achieving current regulation, and the EPTS is furtheroperable to adjust the transmit coil driver circuit to increase the peakmagnitude of the resonant circuit, in response to receiving a respectivemessage from any respective INS requesting an increase in powertransfer.

In some embodiments, the EPTS is further operable to adjust the transmitcoil driver circuit to decrease the peak magnitude of the resonantcurrent, if no respective message requesting an increase in powertransfer from the EPTS has been communicated by any respective INS forat least a certain period of time.

In some embodiments, each respective message includes a request todecrease power transfer from the EPTS if the respective regulatorcircuit is achieving current regulation, and the EPTS is furtheroperable to adjust the transmit coil driver circuit to decrease the peakmagnitude of the resonant current, in response to receiving a respectivemessage from every respective INS requesting a decrease in powertransfer.

In some embodiments, the respective monitoring circuit within eachrespective INS is operable to compare the respective electrode currentprovided by the respective regulator circuit against a respectiveprescribed electrode current for the respective electrode driver circuitcorresponding to a stimulation configuration programmed therein, anddetermine that the respective regulator circuit is achieving currentregulation if the respective electrode current is greater than or equalto the respective prescribed electrode current.

In some embodiments, each respective INS further includes a respectiveresonant rectifier circuit having an input coupled to the respectivereceive coil, and having an output coupled to the input of therespective regulator circuit. The respective resonant rectifier circuitis operable to generate on its respective output a rectified voltage. Insome embodiments each respective INS may further include a respectivede-tuning circuit coupled to the respective receive coil, being operableto de-tune the respective receive coil to inhibit power transfer fromthe EPTS to the respective INS.

In some embodiments, each respective INS further includes a respectivecharge storage device, and each respective regulator circuit is furtheroperable to provide on a second output thereof a charging current to therespective charge storage device. In some embodiments each respectivecharge storage device may be a supercapacitor.

In some embodiments, each respective INS is head-located beneath thedermis layer of a patient.

In another embodiment, a neurostimulation system is provided including apower unit, which includes a variable power generator, a controller tocontrol the output power level of the variable power generator, a powercoupler for coupling power over a dermis layer, and a power sourcetelemetry system for receiving information across a dermis layer forinput to the controller; and an implantable neurostimulator including atleast one neurostimulator lead with at least one array of stimulationelectrodes, an electrode driver for driving the electrodes with adesired power, a power level detector for detecting the output power ofthe electrode driver, a neurostimulator power coupler for coupling powerfrom over a dermis layer, a neurostimulator telemetry system fortransmitting information across the dermis layer to the power sourcetelemetry system, and a processor for determining the amount of powerrequired from the power source as a power demand based on the output ofthe power level detector and transmitting a request for a desired powerlevel to the controller via the telemetry system in the power source;wherein the controller increases or decreases the power level deliveredto the implantable neurostimulator as a function of determined powerdemand by the processor.

In some embodiments, the power unit and neurostimulator power couplerseach include at least one coil. In some of these embodiments, thevariable power generator generates alternating current power. Someembodiments further include a controller which varies the powergenerated by varying a voltage of the variable power generator. In someembodiments, the implantable neurostimulator further includes a chargestorage device. In some embodiments, the power unit power coupler isinductively coupled to the neurostimulator power coupler. In someembodiments, the neurostimulator and the power unit telemetry systemeach communicate information across the dermis layer through therespective power unit and neurostimulator power couplers.

In another embodiment, a system is provided for driving an implantableneurostimulator lead having a plurality of electrodes disposed in atleast one array, the system including an implantable pulse generator(IPG), which includes an electrode driver for driving the electrodes, aload system for determining load requirements of the IPG, an IPG powercoupler for receiving power across a dermis layer for interface of thepower with the electrode driver, and an IPG communication system fortransmitting the load determined requirement of the IPG across thedermis layer. In this embodiment, the system also includes an externalunit, which includes an external variable power generator, an externalpower coupler for coupling power across the dermis layer to the IPGpower coupler, an external communication system for receiving from theIPG communication system the determined load requirements, and acontroller for varying the power level of the variable generator as afunction of the received determined load requirements of the IPG.

In some embodiments, the electrode driver drives the electrodes with aconstant current. In some embodiments, the load system further includesa detector for detecting power delivered to the electrodes and aprocessor for determining the necessary power from the external unitrequired by the electrode driver as the determined load requirements ofthe IPG. In some embodiments, the electrode driver delivers apredetermined constant current. In some of these embodiments, thepredetermined load requirement includes at least enough power from theexternal unit to provide the predetermined constant current from theelectrode driver. In some embodiments, the IPG also includes a chargestorage device. In some embodiments, the IPG is head-located beneath thedermis layer of a patient. In some embodiments, the IPG communicationsystem and the external communication system each include at least onecoil.

In another embodiment, the system is for driving a plurality ofimplantable neurostimulator leads, each lead having an associatedplurality of electrodes disposed in at least on array on the lead. Thesystem includes at least two implantable pulse generators (IPGs), witheach IPG including an electrode driver for driving the electrodesassociated with the IPG, a load system for determining load requirementsof the IPG, an IPG power coupler for receiving power across a dermislayer for interface of the power with the electrode driver of the IPG,and an IPG communication system for transmitting the load determinedrequirement of the IPG across the dermis layer. The system also includesan external unit, which includes an external variable power generator,and external power coupler for coupling power across the dermis layer tothe IPG power couplers, and external communication system for receivingfrom the IPG communication systems the respective determined loadrequirements, and a controller for varying the power level of thevariable power generator as a function of the received determined loadrequirements of the IPG with the greatest load requirement.

In some embodiments, the communication systems of the IPGs are operableto transmit load requirements to the external communication systemindependently of the communication systems of the other IPGs. In someembodiments the IPG communication systems transmit the load determinedrequirements to the external unit communication system inductively. Insome embodiments, the IPG power couplers are for receiving levels ofpower across a dermis layer that are independent of the levels of powerreceived by the power couplers of the other IPGs. In some embodiments,at least one of the IPGs also includes a charge storage device.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail. The details ofvarious implementations are set forth in the accompanying drawings andthe description below. Consequently, those skilled in the art willappreciate that the foregoing summary is illustrative only and is notintended to be in any way limiting of the invention. It is only theclaims, including all equivalents, in this or any non-provisionalapplication claiming priority to this application, that are intended todefine the scope of the invention(s) supported by this application.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to thefollowing description taken in conjunction with the accompanyingDrawings in which:

FIG. 1 depicts a side view of a full Head-Mounted, UnibodyRadiofrequency-Coupled Neurostimulator System for migraine and otherhead pain. The system features an implantable pulse generator (IPG) fromwhich two neurostimulating leads extend—a Frontal-Parietal Lead (FPL)and an Occipital Lead (OL). Each lead includes a plurality of electrodesin a distribution and over a length to allow full unilateral coverage ofthe frontal, parietal, and occipital portions of the head. The IPGcontains all electronics, including an Application Specific IntegratedCircuit (ASIC) and an RF Receiver Coil that is capable of an RF coupleto an External Power Source and Programming Unit;

FIG. 1A illustrates an embodiment of the IPG 10 and the variousconfigurations of the lead;

FIG. 1B illustrates an embodiment of the IPG 10 and the variousconfigurations of the lead;

FIG. 2 depicts a side view of a Frontal Electrode Array (FEA) withInternal Wires. The FEA is disposed over the distal portion (such as8-10 cm) of the FPL, which anatomically places it over the frontalregion, and specifically over the supraorbital nerve and other adjacentnerves of the region. In general the layout, disposition and connectionsof the Internal Wires and Surface Electrodes disposed over the ParietalElectrode Array (PEA) and the Occipital Electrode Array (OEA) are thesame as that depicted for the FEA;

FIG. 3 depicts a side view of an IPG, along with its enclosed ASIC, RFReceiver Coil, and Internal Magnet, along with the Internal Wiresexiting from the IPG's Internal Circuit enroute to the SurfaceElectrodes disposed over the FPL and the OL;

FIG. 3A depicts a more detailed view of the internal structure of anIPG;

FIG. 4 depicts a cross-sectional view of a Lead Central Body comprisinga Cylindrical Lead Body (with Internal Wires) between the IPG InternalCircuit and the Lead Surface Electrodes;

FIG. 5 depicts a rear view of a Head with a full Head-LocatedNeurostimulator System In-Situ. Prominent here is the OL depictedpassing from the IPG caudally and medially across the occipital region,whereby the OEA is disposed in a fashion to cross over and cover themajor associated nerves—primarily the greater occipital nerve, buttypically including the lessor and/or third occipital nerve as well.Also depicted are the PEA and the FEA of the FPL as they cross and coverthe primary nerves of the Parietal Region, including theauriculo-temporal nerve, and the Frontal Region, including thesupraorbital nerve. Also depicted is the IPG with its Internal Circuit,Internal RF Receiver Coil, and ASIC;

FIG. 6 depicts a side view of a Head with a full Head-Located, UnibodyRadiofrequency-Coupled Neurostimulator System In-Situ. Prominent here isthe PEA, as it covers a portion of the Parietal Region 60 and the majorassociated nerves, including the auriculo-temporal nerve 61 as well asother adjacent cutaneous nerves. The frontal region of the head andsupraorbital nerve 71 are also depicted. Also depicted are the coursesof the distal portion of the FPL and the OL, as they pass over and coverthe associated nerves of the Frontal (Supraorbital) and OccipitalRegions. Also depicted is the IPG including its Internal Circuit, ASIC,and RF Receiver Coil;

FIG. 7 depicts a front view of a Head with a full Head-Located, UnibodyRadiofrequency-Coupled Neurostimulator System In-Situ. Prominent here isthe FEA, as it covers a portion of the Frontal (Supraorbital) Region andthe major associated nerves—primarily the supraorbital nerve, but alsocommonly the greater trochlear nerve, as well as adjacent nerves. Alsodepicted is the course of the parietal portion of the FL. Also depictedis the IPG including its Internal Circuit, ASIC, and RF Receiver Coil;

FIG. 8 depicts a side view of the External “Behind the Ear” Assembly.Prominent here is the IPG with its IPG including its Internal Circuit,ASIC, and RF Receiver Coil. The External Assembly includes the ExternalEarl Clip, the Behind-the-Ear Electronics and Battery Component, theExternal Coil Lead, and the External RF Coil Plastic Housing, whichcontains the External RF Coil and External RF Magnet;

FIG. 9 depicts right oblique front view of a head with a fullHead-Located, Unibody Radiofrequency-Coupled Neurostimulator SystemIn-Situ, along with an External “Behind the Ear” Assembly. Prominenthere is the IPG with its IPG including its Internal Circuit, ASIC, andRF Receiver Coil. The External Assembly includes the External Earl Clip,the Behind-the-Ear Electronics and Battery Component, the External CoilLead, and the External RF Coil Plastic Housing, which contains theExternal RF Coil and External RF Magnet;

FIG. 10 is a block diagram of a system that provides for independentcharge transfer and communication with multiple implanted devices, inaccordance with some embodiments of the invention;

FIG. 11 is a block diagram of a system depicting the de-tuning of areceive coil within an implanted device to selectively turn offcharging, in accordance with some embodiments of the invention;

FIG. 12 is a block diagram of a system which provides for datacommunication (forward telemetry) and power transmission to an implanteddevice using opposite polarity half-wave rectified signals received bythe implanted device, in accordance with some embodiments of theinvention;

FIG. 13A is a block diagram of a system which provides forbi-directional communication with an implanted device, and particularlyillustrates passive communication from an implanted device (backtelemetry) when the receive coil is de-tuned, in accordance with someembodiments of the invention;

FIG. 13B illustrates voltage waveforms of selected signals depicted inthe embodiment shown in FIG. 13A;

FIG. 14A is a block diagram of a system which includes charge transfercoil (or “transmit coil”) current sensing circuitry to determine backtelemetry data received from an implanted device, and to determinede-tuning of an implanted device coil, in accordance with someembodiments of the invention;

FIG. 14B illustrates voltage waveforms of selected signals depicted inthe embodiment shown in FIG. 14A;

FIG. 15 is a block diagram of a system which provides for adjustabletransmitted power to improve power efficiency within an implanteddevice, in accordance with some embodiments of the invention;

FIG. 16A is a block diagram of a system which includes feedbackexcitation control of a resonant coil driver amplifier, in accordancewith some embodiments of the invention.

FIG. 16B illustrates voltage waveforms of selected signals depicted inthe embodiment shown in FIG. 16A;

FIG. 17 is a block diagram of a headset that includes an external chargetransfer system for two implanted devices, in accordance with someembodiments of the invention;

FIG. 18, which includes FIGS. 18A and 18B, is a schematic diagram of anexemplary IPG driver and telemetry circuitry block, such as that shownin FIG. 17, in accordance with some embodiments of the invention;

FIGS. 19A, 19B, and 19C illustrate voltage waveforms of selected signalsdepicted in the embodiment shown in FIG. 18 and FIG. 23A;

FIG. 20 is a schematic diagram of an exemplary headset buck/boostvoltage generator circuit, such as that shown in FIG. 8, in accordancewith some embodiments of the invention;

FIG. 21 is a block diagram of a body-implantable active device, inaccordance with some embodiments of the invention;

FIG. 22A illustrates a simplified block diagram of the IPG;

FIG. 22B illustrates a flow chart for the operation of the initiation ofa neurostimulation program at the IPG;

FIG. 23A is a schematic diagram of an exemplary rectifier circuit andtelemetry/de-tune circuit, such as those shown in FIG. 21, in accordancewith some embodiments of the invention;

FIG. 23B illustrates voltage waveforms of selected signals depicted inthe embodiment shown in FIG. 23A;

FIG. 24 is a schematic diagram of portions of an exemplary boostcircuit, such as that shown in FIG. 21, in accordance with someembodiments of the invention;

FIG. 25 is a diagram representing an exemplary headset that includes anexternal charge transfer system for two separate body-implantabledevices, each implanted behind a patient's respective left and rightears, and shows an associated headset coil placed in proximity to thecorresponding receive coil in each implanted device;

FIG. 26 depicts two implanted IPGs with leads to cover both sides of thehead;

FIG. 27 depicts one implanted IPG with leads to cover both sides of thehead;

FIG. 28 illustrates the embodiment of FIG. 26 with acharging/communication headset disposed about the cranium;

FIG. 29 illustrates a diagrammatic view of the power regulation systemand current regulation system on the IPG;

FIG. 30 illustrates a diagrammatic view of the voltage chargingrelationships for the supercapacitor; and

FIG. 31 illustrates a flowchart for power transfer system from theheadset.

DETAILED DESCRIPTION A. Introduction

Referring now to the drawings, wherein like reference numbers are usedherein to designate like elements throughout, the various views andembodiments of an implantable neurostimulation lead for head pain areillustrated and described, and other possible embodiments are described.The figures are not necessarily drawn to scale, and in some instancesthe drawings have been exaggerated and/or simplified in places forillustrative purposes only. One of ordinary skill in the art willappreciate the many possible applications and variations based on thefollowing examples of possible embodiments.

The present disclosure provides for a fully head-located,radiofrequency-coupled, implantable peripheral neurostimulation systemthat is specifically designed for the treatment of chronic head pain. Itincorporates multiple unique elements and features that take intoaccount the unique anatomic, physiologic, and other related challengesof treating head pain with implantable neurostimulation and, by doingso, greatly improves on therapeutic response, patient safety, medicalrisk, and medical costs, which combine to improve overall patientsatisfaction.

Prior implantable peripheral neurostimulation systems and components,including leads and pulse generators, had been originally designed anddeveloped specifically as spinal cord stimulator systems and for thespecific therapeutic purpose of treating chronic back and extremitypain. Over the years, however, these spinal cord stimulators wereultimately adopted and adapted for use as implantable peripheral nervestimulators for the treatment of migraine headaches and other forms ofchronic head pain. However, they were so utilized with full recognitionof the inherent risks and limitations due to the fact that they had beendeveloped to only address, and accommodated to, the unique anatomic andphysiologic features of the back and chronic back pain.

A number of problems have been recognized with respect to spinal cordstimulators for head pain as fundamentally due to design flawsassociated with, and inherent to, the use of an implantable therapeuticdevice in an area of the body that it was not designed for.

The anatomy of the head and the pathophysiology of headaches and otherforms of head pain are so significantly different from the anatomy ofthe spinal canal and pathophysiology of chronic back pain, that whenspinal cord stimulators are utilized for cranial implants, the clinicalproblems associated with these differences manifest themselves.Importantly, these well-documented problems are clinically verysignificant and include issues of patient safety and satisfaction, therisk of an inadequate or suboptimal therapeutic response, issues withpatient comfort and cosmetics, and a recognized increased risk ofsurgical complications and technical problems.

Prior implantable peripheral neurostimulation leads have been designedand developed specifically for placement in the spinal canal as part ofa spinal cord stimulation system and for the specific therapeuticpurpose of treating various forms of chronic back and extremity pain.The present disclosure provides an implantable peripheralneurostimulation lead that is designed for the implantation in the headfor the treatment of chronic head pain. It incorporates multiple uniqueelements and features that take into account the unique anatomic,physiologic, and other related challenges of treating head pain withimplantable neurostimulation and by doing so greatly improves ontherapeutic response, patient safety, medical risk, medical costs, whichcombine to improve overall patient satisfaction.

Indeed, the anatomy of the head, and the pathophysiology of headachesand other forms of head pain that are unique to the head, are sosignificantly different from the anatomy of the spinal canal, andpathophysiology of chronic back pain that when these current leads areindeed utilized as cranial implants, then the clinical problemsassociated with these differences manifest themselves. Specifically,these include issues with inadequate therapeutic responses, issues withpatient comfort and cosmetics, and also very significant issues withpatient safety.

These medical risks stem from the design of conventional leads and theIPG. Conventional lead designs include a relatively large diameter, acylindrical shape, (often) inadequate length, and the necessity ofimplanting the IPG in the torso and distant from the distal leads, and anumber and disposition of the surface electrodes and active lead arraysthat do not match the requirements. A cylindrical lead of relativelylarge diameter results in increased pressure on, and manifest tentingof, the overlying skin, particularly of the forehead. Becauseconventional leads are of inadequate length to extend from the head tothe IPG implant site, commonly in the lower back, abdomen, or glutealregion, lead extensions are often employed, and there are attendantrisks of infection, local discomfort, and cosmetic concerns.

With respect to prior leads: 1) There is only a single array ofelectrodes, with common lead options including 4, 8, or 16 electrodesdisposed over that single array; 2) The array is relatively short withmost leads having an array of from 5-12 cm in length; 3) Within thissingle array, the individual electrodes are disposed uniformly withconstant, equal inter-electrode distances. This results in the need toimplant multiple (often four or more) of the conventional leads toadequately cover the painful regions of the head.

There are several practical clinical outcomes that result from the useof prior leads for the treatment of chronic head pain. First, since theycomprise a single, relatively short active array, the currentlyavailable leads provide therapeutic stimulation to only a single regionof the head; that is, they can provide stimulation to only the frontalregion, or a portion of the parietal region, or a portion of theoccipital region. Therefore, if a patient has pain that extends overmultiple regions, then multiple separate lead implants arerequired—basically one lead implant is required for each unilateralregion. A great majority of patients with chronic headaches experienceholocephalic pain; that is they experience pain over the frontal andparietal and occipital regions bilaterally. Therefore, commonly thesepatients will need 4 to 7 leads implanted to achieve adequatetherapeutic results (2 or 3 leads on each side).

Second, the need for multiple leads includes considerable added expense,and more importantly, added medical risk associated with adverse eventsattendant to the multiple surgical procedures. Such adverse eventsinclude an increased risk of infection, bleeding, and technical issueswith the leads, e.g., lead fracture, lead migration, and localirritation.

Third, as the clinical database discloses, the inter-electrode spacingmay be of central therapeutic significance. That is, for example,whereas commonly pain over the occipital region is consistentlyeffectively treated by quadripolar leads (leads with four evenly spacedelectrodes) that have the electrodes relatively widely spaced apart(approximately a cm or more apart), clinically it is often found thatelectrodes configurations that are more narrowly spaced may be moreeffective over the supraorbital nerve and regions. Thus, a quadripolarlead that has the electrodes only 1-2 mm apart may be more effective inthis region, as it allows for more precise control of the deliveredelectrical pulse wave delivery.

When an IPG implant for spinal cord stimulation systems is employed as aperipheral nerve stimulator for head pain, several outcomes result.First, the IPG is implanted at a considerable anatomic distance from thecranial lead implants. Indeed, the leads must pass from their distalcranial implant positions across the cervical region and upper back tothe IPG implant location, which are most commonly in the lower back,lower abdomen, or gluteal region. The leads must cross multiple anatomicmotion segments, including the neck and upper back and/or chest at aminimum, and commonly include the mid back, lower back and waistsegments, as well. The simple motions of normal daily life produceadverse tension and torque forces on the leads across these motionsegments, which in turn increases the risk of various outcomes includinglead migration and/or lead fracture. In addition, the relatively largesize of a spinal cord stimulator IPG contributes to local discomfort,cosmetic concerns, and increased risk of infection that may becomelarger and harder to treat in proportion to the size of the IPG pocket.

The present disclosure is directed to an implantable neurostimulationsystem that includes an IPG from which two neurostimulating leads extendto a length sufficient to allow for therapeutic neurostimulationunilaterally over the frontal, parietal and occipital regions of thehead.

The present disclosure addresses and effectively solves problemsattendant to publically available leads. The most important of these isthe fact that currently available leads can only adequately stimulate asingle region of the head due to design element flaws associated withterminal surface electrode number and disposition. The disclosureadditionally addresses and solves other problems inherent with thecurrently available leads, including problems with cosmetics and patientcomfort, particularly over the frontal regions, due the uncomfortablepressure placed on the skin of the forehead, due the cylindrical shapeand relatively large diameter of the distal portion of the lead.Finally, the lead of the present disclosure solves the currentlyavailable leads' problem of inadequate lead length to reach a gluteallocation of the implantable pulse generator, which thereforenecessitates the additional risk and expense of further surgery toimplant lead extensions.

In one aspect, the implantable, head-mounted, neurostimulation systemfor head pain is operable for subcutaneous implantation in the head, andto provide neurostimulation therapy for chronic head pain, includingchronic head pain caused by migraine and other headaches, as well aschronic head pain due other etiologies. The peripheral neurostimulatorsystem disclosed herein takes into account unique anatomic features ofthe human head, as well as the unique, or singular, features of thevarious pathologies that give rise to head pain, including migraine andother headaches, as well as other forms of chronic head pain. To date,all commercially available leads and systems that have been clinicallyutilized for implantation as a peripheral neurostimulator lead wereactually originally designed specifically for placement in the epiduralspace, as part of a spinal cord stimulation system, for the therapeuticpurpose of treating chronic back and/or extremity pain. Thus, there arecurrently no commercially available leads or full system that havedesigns in the public domain, that have been designed and developed foruse in the head and for head pain.

In another aspect, the implantable, head-mounted, neurostimulationsystem for head pain comprises multiple design features, includingdisposition of a sufficient plurality of surface electrodes over asufficient linear distance along the distal lead, such as will result ina lead that, as a single lead, is capable of providing medicallyadequate therapeutic stimulation over the entire hemicranium; that is,over the frontal, parietal, and occipital region stimulation. Currentlyavailable systems, which were designed specifically for epiduralplacement for chronic back pain, are capable of only providingstimulation over a single region; that is, over either the frontalregion alone, or the parietal region alone, or the occipital regionalone.

In yet another aspect, the implantable peripheral neurostimulationsystem for head pain comprises multiple design features, including thephysical grouping of the extended array of surface electrodes into threeor more discrete terminal surface electrode arrays. The linear layout ofthese two or more (preferrably three or more) surface electrodes arraysis designed such that following implantation there would be at least onearray positioned over the frontal region, at least one array positionedover the parietal region, and at least one array positioned over theoccipital region. This feature further improves upon therapeuticeffectiveness of the extended terminal surface electrode arraysufficient for hemicranial stimulation by allowing for more precisecontrol of the therapeutic neurostimulation parameters.

In still another aspect, the implantable, head-mounted, neurostimulationsystem for head pain comprises multiple design features, includingincorporating individual design features within each of the three ormore individual surface electrode arrays. Examples of such intra-arraydesign features would include the specific number of electrodes allottedto each group; whether the electrodes are cylindrical or flattened; thewidth of each electrode within each array, and the linear distanceintervals of separation of the electrodes within each array. Thisfeature further improves upon therapeutic effectiveness of the extendedterminal surface electrode array sufficient for hemicranial stimulation,and the grouping of these electrodes into three or more separate surfaceelectrode arrays, by providing each specific array location a uniqueintra-array design that takes into account, and thereby seeks tooptimizes, design elements that are known to be possibly or likelybeneficial to the therapeutic end result, given the anticipatedpost-implant anatomic location of that array.

In yet another aspect, an implantable peripheral neurostimulation systemfor head pain comprises multiple novel design features, includingincorporating individual design features into a single lead design andthereby achieving additive benefits.

In still another aspect, an implantable peripheral neurostimulationsystem for head pain results in a marked decrease in the number ofseparate lead implants required to adequately treat a single patient. Asingle implant will provide the same therapeutic anatomic coverage thatit would take for the implantation of three or four of the currentlyavailable leads. That is, instead of the current which often calls forthree or more leads to be implanted to provide adequate hemicranialcoverage, the same anatomic region may be covered with a singlestimulator lead implant. The lead provides extended coverage over thefull hemicranium; that is, achieving medically acceptableneurostimulation unilaterally over the frontal, parietal, and occipitalregions simultaneously. In contrast, publically known leads are able toconsistently provide medically acceptable neurostimulation therapy onlyover a single region, meaning that it would require three separatesurgically lead implants to achieve the same therapeutic coverage of asingle implant of a lead of the present disclosure. This will decreasethe total number of surgeries required, as well as the extent of eachindividual surgery for many patients.

In another aspect, by having a system that is fully localized to thehead, it eliminates the requirement of currently available systems ofhaving long leads and extensions extending across the neck and back toIPG locations commonly in the low back and gluteal region, and therebydecreases the risk of problems attendant to such long leads andextensions, including discomfort, infection, technical extension issuessuch as fracture, and other morbidities. This results in a furtherdecrease in the number of surgeries required by a patient.

In other aspects, an IPG may be of proper aspect ratio with respect tothe specific site of intended implantation in the head, preferably anarea posterior to and/or superior to the ear. There may be an externalportable programming unit that is capable of achieving a radiofrequencycoupling to the implanted unit. An IPG may have an internal RF receivercoil that is capable of coupling via a radiofrequency mechanism to anexternal control unit that provides power and control function. An IPGmay contain an internal RF receiver, an application specific integratedcircuit, and a supercapacitor. In the event the external power supply islost, the supercapacitor can supply power to the device and keep thedevice functioning until the external power connection can be resumed.The system may include a primary cell as a power source. An IPG may becapable of being multiplexed, i.e., the IPG can be programmed to onlystimulate (turn on) the required and necessary electrical contactsneeded for therapy and turn off the ones not needed.

In other aspects, the system may include one or more of the followingfeatures. A neurostimulating lead may not require a central channel fora stylet. A neurostimulating lead may have a smaller diameter thancurrently available leads. A neurostimulating lead may have a shaped orflat electrode design that orients the electrical fields toward thespecific nerves, thus avoiding stimulation of undesired tissues, e.g.,adjacent muscles, while additionally improving patient cosmetics. Aneurostimulating lead may include redundant electrodes for the shaped orflat electrode contacts such that in the event the leads areinadvertently flipped, these redundant electrodes can be selected andactivated so that the electric fields can still be oriented at theproper nerves.

In other aspects, the system may include one or more of the followingfeatures. The system may include the disposition of a sufficientplurality of surface electrodes over a sufficient linear distance alongthe system's leads to enable medically adequate therapeutic stimulationacross multiple regions of the head, and preferably the entirehemicranium; that is, over the frontal, parietal, and occipital regionsimultaneously. The extended array of surface electrodes may be dividedinto two or more discrete terminal surface electrode arrays. Thepreferred linear layout of these multiple surface electrode arraysincludes at least one array positioned over the frontal region, at leastone array positioned over the parietal region, and at least one arraypositioned over the occipital region.

In other aspects, intra-array design features may include variations inthe specific number of electrodes allotted to each group; the shape ofthe electrodes, e.g., whether the electrodes are cylindrical orflattened; the width of each electrode within each array, and the lineardistance intervals of separation of the electrodes within each array.

In other aspects, the system may include a plurality of connection portsthat can be connected with a plurality of leads and thus allow forattaching additional leads should they later be required.

In another aspect, an implantable peripheral neurostimulation system forhead pain comprises multiple design features; including features aimedat improving patient safety by improving the incidence of adverseevents, including the risk of infection, as well as the risk andincidence of known technical problems associated with implanted leads,including lead migration and lead fracture, amongst others. The lead maycomprise two or more (i.e. three or more) surface electrode arrays, eachuniquely designed, that are disposed over a sufficient lead length toallow for medically acceptable therapeutic neurostimulator coverage ofat least regions within the supraorbital, parietal, and occipitalcranial regions. To achieve the same clinical coverage from a singleimplant, it would require three or more separately surgically implantedleads. Therefore, by reducing the number of surgical incisions, as wellas the number of surgically implanted leads, the associated risks ofadverse events are proportionally diminished.

In yet another aspect, an implantable peripheral neurostimulation systemfor head pain may treat chronic head and/or face pain of multipleetiologies, including migraine headaches; and other primary headaches,including cluster headaches, hemicrania continua headaches, tension typeheadaches, chronic daily headaches, transformed migraine headaches;further including secondary headaches, such as cervicogenic headachesand other secondary musculokeletal headaches; including neuropathic headand/or face pain, nociceptive head and/or face pain, and/or sympatheticrelated head and/or face pain; including greater occipital neuralgia, aswell as the other various occipital neuralgias, supraorbital neuralgia,auroiculotemporal neuralgia, infraorbital neuralgia, and othertrigeminal neuralgias, and other head and face neuralgias.

In another aspect, an implantable, head-mounted, neurostimulation systemfor head pain comprises multiple design features, including featuresaimed at improving patient safety by improving the incidence of adverseevents, including the risk of infection, as well as the risk andincidence of known technical problems associated with implanted leads,including lead migration and lead fracture, amongst others. The lead maycomprise two or more (i.e. three or more) surface electrode arrays, eachuniquely designed, that are disposed over a sufficient lead length toallow for medically acceptable therapeutic neurostimulator coverage ofat least regions within the supraorbital, parietal, and occipitalcranial regions. To achieve the same clinical coverage from a singleimplant, it would require three or more separately surgically implantedleads. Therefore, by reducing the number of surgical incisions, as wellas the number of surgically implanted leads, the associated risks ofadverse events are proportionally diminished.

In yet another aspect, an implantable, head-mounted, neurostimulationsystem for head pain may treat chronic head and/or face pain of multipleetiologies, including migraine headaches and other primary headaches,including cluster headaches, hemicrania continua headaches, tension typeheadaches, chronic daily headaches, transformed migraine headaches,further including secondary headaches, such as cervicogenic headachesand other secondary musculoskeletal headaches, including neuropathichead and/or face pain, nociceptive head and/or face pain, and/orsympathetic related head and/or face pain, including greater occipitalneuralgia, as well as the other various occipital neuralgias,supraorbital neuralgia, auroiculotemporal neuralgia, infraorbitalneuralgia, and other trigeminal neuralgias, and other head and faceneuralgias.

In other aspects, an implantable, head-mounted, neurostimulation systemfor head pain may not require a central channel for stylet placementover its distal (frontal) portions. The lead may improve patient comfortand cosmetics by virtue of its relatively small diameter over the distalportions of the lead, partially due the lack of a central styletchannel, as well as due to a progressive decrease in the number ofinternal wires continuing after each terminal electrode. The lead mayfurther improve cosmetic appearance and patient comfort by incorporatinga flattened lead design for that portion of the lead expected to be overthe frontal portion of the head.

Thus, the present disclosure provides for a peripheral neurostimulationlead that is uniquely designed for implantation in the head as a therapyfor chronic head pain, and is designed to solve the known design issuesassociated with current leads, as the lead of the present disclosureseeks to optimize the therapeutic response, improve patient comfort,improve cosmetics, reduce the number of surgical leads required, andreduce medical risk, and reduce medical costs.

B. Overview

Turning now descriptively to the drawings, in which similar referencecharacters denote similar elements throughout the several views, thefigures illustrate an implantable pulse generator (IPG) from which twoneurostimulating leads may extend to a length sufficient to allow fortherapeutic neurostimulation unilaterally over the frontal, parietal andoccipital regions. The leads include an extended plastic lead body, aplurality of surface metal electrodes disposed along the lead, which maybe divided into two or more electrode arrays, a plurality of internalelectrically conducting metal wires running along at least a portion ofits length and individually connecting the IPG's internal circuit toindividual surface metal electrodes. The implantable pulse generatorincludes the internal circuits, a radiofrequency receiver coil, and anASIC. The system may be operable to provide medically acceptabletherapeutic neurostimulation to multiple regions of the head, includingthe frontal, parietal and occipital regions simulataneously, and sixfigures demonstrate various views of this feature as the system isdepicted in situ.

C. Full Head-Located Neurostimulator System

FIG. 1 depicts a side view of a full neurostimulator system, whichconsists of an implantable pulse generator (IPG) 10 along with twounibody plastic lead extensions—a Fronto-Parietal Lead (FPL) 20 and anOccipital Lead (OL) 30 of adequate length to extend to roughly themidline of the forehead and to the midline at the cervico-cranialjunction, respectively. Arrows 28 indicate the point of cross section ofFIG. 4.

FIGS. 5, 6, and 7 depict posterior, lateral and frontal views of thesystem in-situ. The unit is demonstrated in an implant position wherethe IPG 10 is posterior and cephalad to the pinna of the ear. Thedrawings demonstrate the FPL 20 passing over the parietal 60 and frontal70 regions of the head, including auriculo-temporal nerve 61 andsupraorbital nerve 71, in a manner that places the FEA over thesupraorbital nerve and the PEA over the auriculotemporal nerve. The OL30 is shown passing caudally and medially over the occipital region ofthe head such that the OEA 35 cross over the greater occipital nerve 51,the lesser occipital nerve 52, and the third occipital nerve.

FIGS. 8 and 9 depict two views of the external control unit (ECU) 100.FIG. 8 depicts a side view of an ECU 100, the components of whichinclude an ear clip 1110, an electronics and battery component (EBC)1120, an external coil lead 1130, and an external RF coil housing 1140that contains a RF coil 1141 external magnet 1142. FIG. 9 depicts aright oblique frontal view of the head with an implantableneurostimulator system in-situ, and with the ECU 100 attached to the earin its functional position, with the external RF coil housing 1140 inposition opposite the internal RF coil 11 and internal magnet 12 of theIPG 10.

D. Fronto Parietal Lead

Continuing with FIG. 1, the FPL 20, as part of the unibody construction,extends from the IPG. The FPL comprises a plastic body member 20 a and aset of internal conducting wires 29.

The plastic body member 20 a is an elongated, cylindrical, flexiblemember, which may be formed of a medical grade plastic polymer. It has aproximal end 22, a distal end 21, and may be conceptually divided intofive segments along its linear dimension. Progressing from the proximalend 22, these segments sequentially include a proximal lead segment(PLS) 22 a, a parietal electrode array (PEA) 26, an inter-array interval27, a frontal electrode array (FEA) 25, and a distal non-stimulating tip23.

The lead internal wires 29 pass along the interior of the plastic bodymember as depicted in FIG. 4.

E. Frontal Electrode Array

Continuing with FIG. 1, the FEA 25 consists of a plurality of surfacemetal electrodes (SME) 24 uniformly disposed over a portion of thedistal aspect of the FPL 20. Lead internal wires 29 connect to the SME24 as depicted in FIG. 2, which represents the distal four SME 24 of thelead.

F. Parietal Electrode Array

Returning to FIG. 1, the PEA 26 consists of a plurality of SME 24uniformly disposed along a linear portion of the FPL. The PEA 26 isseparated along the FPL from the FEA by an inter-array interval 27. Itis separated only the lead from the IPG by the PLS 22 a. The leadinternal wires 29 connect to the individual SMEs 24 of the PEA in thesame fashion as the do with the SME of the FEA as shown in FIG. 2.

G. Occipital Lead

Continuing with FIG. 1, the occipital lead (OL) 30 as part of theunibody construction extends from the IPG 10. It comprises a plasticbody member 39 and a set of lead internal wires 38 that pass through thecentral cylinder of the lead to connect to a series of SME 34, each ofsurface electrode width 37, that are uniformly disposed at aninterelectrode distance 36 from each other along a portion of the lengthof the lead. These lead internal wires 38 pass and connect in the samemanner as described above for the SME 24 of the FEA 25 as depicted inFIGS. 2 and 4.

The plastic body member 39 is an elongated, cylindrical, flexiblemember, which may be formed of a medical grade plastic polymer. It has aproximal end 32 and a distal end 31. Progressing along the lead from theproximal end 32, these segments sequentially include a proximal leadsegment (PLS) 32 a, an occipital electrode array (OEA) 35, and a distalnon-stimulating tip 23.

H. Occipital Lead Array

As depicted in FIG. 1, the OEA 35 consists of a plurality of surfacemetal electrodes (SME) 34 uniformly disposed over a portion OL 30. Leadinternal wires 38 connect to the SME 24 in the same fashion as depictedfor the FEA 25 as shown in FIG. 2.

I. Implantable Pulse Generator

Referring to FIG. 1 and FIG. 3, the three primary physical andfunctional components of the IPG 10 include an internal magnet 12, aninternal radiofrequency receiver coil 11, and an application specificintegrated circuit (ASIC) 13, along with the necessary internal wireconnections amongst these related components, as well as to the incominglead internal wires 29, 39. These individual components may be encasedin a can made of a medical grade metal and plastic cover 14, whichitself transitions over the exiting FPL 20 and OL 30.

Referring now to FIGS. 1A and 1B, there are illustrated embodiments ofthe IPG 10 and the various configurations of the lead. In FIG. 1A, theFPL lead 20 and the OL lead 30 are illustrated as extending downwardfrom the IPG body 10. In FIG. 1B, the coil 11 and the magnet 12 aredisposed in a separate body 10′ that is disposed distal from theintegrated circuit 13 or ASIC 13 by a lead 20′. This allows the coil 11to be disposed at a point in the hemicranium distal from the ASIC 13.For implantation, the magnet 12 is removed therefrom and the body 10′ is“rolled up” in a tube with the approximate diameter of the lead 20′,such that it can be routed subcutaneously to a different location aboutthe head. This is to facilitate coupling with an external coil in a morecomfortable manner for the patient.

J. External Controller

FIG. 8 depicts an external “behind the ear” controller (EC) 100, whichincludes an ear clip 1110, an electronics and battery component (EBC)1120, an external coil lead 1130 and an external RF coil plastic housing(ECPH) 1140, which contains the external RF coil 1141, and the externalmagnet 1142.

FIG. 9 depicts a right oblique frontal view of the head with an in-situfull neurostimulator system. The EC 100 is depicted as secured intoposition by an ear clip 1110, and the ECPH 1140 is depicted as appliedto the skin directly over the internal radiofrequency receiver coil 11and internal magnet 12 components of the IPG 10.

K. Connections of Main Elements and Sub-Elements

The system may include a unibody construction to provide physical andfunctional continuity of the related components and sub-components.

The overall mechanistic purpose of an implantable neurostimulationsystem is to generate and conduct a prescribed electrical pulse wavefrom an IPG 10 down a set of lead internal wires 29, 38 running aportion of the length of the lead to specified programmed set of SMEs24, 34, whereby the current is then conducted by tissue and/or fluid toan adjacent, or nearby, set of one or more SME 24, 34, which in turnpasses the signal proximally down the lead wire 29, 38 back to the IPG10 and its ASIC 13, thus completing the circuit.

An external control unit (ECU) 100 provides power, programming anddiagnostic functionality to the implanted neurostimulator system via aradiofrequency couple between the external RF coil 1141 and internal RFcoil 1142. The ECU 100 is held in place on the head by an ear clip 1110,and its ECPH 1140 is held in place over the IPG 10 by internal andexternal magnets 12, 1142.

L. Charge Transfer/Communication Control

FIG. 10 depicts a conceptual diagram of a system 500 that provides forindependent charging/powering and communication with multiplebody-implanted pulse generating (IPG) devices requiring external powerto either power the IPGs directly or to charge an internalsupercapacitor associated with the IPGs or a hybrid thereof. For thepurposes of this disclosure, charge provided to the IPGs will bereferred to as “charge transfer,” but it should be understood that thiscould mean charging of a supercapacitor or delivering charge to apowered element associated with the IPGs. Three charge receiving systems520, 540, 560 are shown, each disposed within a corresponding IPG (notshown). An external charge transfer system 502 disposed outside a dermislayer (or “dermal layer”) 518 includes series-connected charge transfercoils, of which three are shown, being series-connected charge transfercoils 510, 511, 512, each of which corresponds to a respective one ofreceive coils 521, 541, 561 of respective ones of a plurality of chargereceiving systems, of which three are shown, being charge receivingsystems 520, 540, 560. Preferably each receive coil 521, 541, 561 istuned to the resonant frequency of the respective charge transfer coil510, 511, 512 within the external charge transfer system 502. Whilethree charge transfer coils 510, 511, 512 are shown, one for each chargereceiving system 520, 540, 560, other embodiments may utilize one chargetransfer coil, two charge transfer coils, or another number of chargetransfer coils, depending upon the number of IPGs.

The external charge transfer system 502 includes a driver 504,responsive to a DRIVER CTRL signal on node 503, for driving theseries-connected coils 510, 511, 512 with an AC signal. A TX/RXtelemetry block 506 includes a transmitter for transmitting forwardtelemetry data signal within the AC signal driven across the chargetransfer coils (i.e., on node 508), and a receiver to detect and receivea back telemetry data signal within the AC signal. The forward/backtelemetry data signals, both as represented by the DATA signal on node505, are coupled from/to telemetry circuitry within remaining portionsof the external charge transfer system (not shown). As used herein, datacommunication from an external charge transfer system to an IPG isreferred to as forward telemetry, and data communication from an IPG toan external charge transfer system is referred to as back telemetry.

Within the first IPG, the charge receiving system 520 includes a receivecoil 521 that is tuned to the resonant frequency of the associatedcharge transfer coil 510 within the external charge transfer system 502,so that receive coil 521 may receive energy transferred from the chargetransfer coil 510 when in close proximity thereto. The receive coil 521is coupled to a charge receiving block 528 that includes circuitry forreceiving energy in a first mode of operation, and for de-tuning thereceive coil 521 in a second mode of operation to inhibit transfer ofenergy. The receive coil 521 is also coupled (via node 522) to an RX/TXtelemetry block 523 that includes a receiver for receiving a forwardtelemetry data signal from the receive coil 521, and a transmitter fortransmitting a back telemetry data signal to the receive coil 521. Thereceived energy is coupled to charge transfer circuitry, and theforward/back telemetry data signals are coupled to/from data circuitrywithin the first IPG, both as represented by node 529. As can beappreciated, the receive coil 521 serves as a “shared antenna” for boththe charge transfer system and the telemetry system.

Similarly, the charge receiving system 540 includes a receive coil 541that is tuned to the resonant frequency of the associated chargetransfer coil 511, so that receive coil 541 may receive energytransferred from the charge transfer coil 511 when in close proximitythereto. The receive coil 541 is coupled to a charge receiving block 548that includes circuitry for receiving energy in the first mode ofoperation, and for de-tuning the receive coil 541 in the second mode ofoperation to inhibit transfer of energy. The receive coil 541 is alsocoupled (via node 542) to an RX/TX telemetry block 543 that includes areceiver for receiving a forward telemetry data signal from the receivecoil 541, and a transmitter for transmitting a back telemetry datasignal to the receive coil 541. The received energy is coupled to chargetransfer, and the forward/back telemetry data signals are coupledto/from data circuitry within the second IPG, both as represented bynode 549.

Likewise, the charge receiving system 560 includes a receive coil 561that is tuned to the resonant frequency of the associated chargetransfer coil 512, so that receive coil 561 may receive energytransferred from the charge transfer coil 512 when in close proximitythereto. The receive coil 561 is coupled to a charge receiving block 568that includes circuitry for receiving energy in the first mode ofoperation, and for de-tuning the receive coil 561 in the second mode ofoperation to inhibit transfer of energy. The receive coil 561 is alsocoupled (via node 562) to an RX/TX telemetry block 563 that includes areceiver for receiving a forward telemetry data signal from the receivecoil 561, and a transmitter for transmitting a back telemetry datasignal to the receive coil 561. The received energy is coupled to chargetransfer circuitry, and the forward/back telemetry data signals arecoupled to/from data circuitry within the third IPG, both as representedby node 569.

Even though a single driver circuit 504 is utilized to drive all threeseries-connected charge transfer coils 510, 511, 512, the system 500provides for independent charge transfer (or charge delivery) ofmultiple IPGs. When such charge transfer of one of the IPGs is complete(or delivery of charge), the corresponding de-tuning circuitry withinthe respective charge receiving circuit 528, 548, 568 may be activatedto de-tune its respective receive coil 521, 541, 561 and thereby inhibitfurther transfer of energy to the respective charge receiving circuit528, 548, 568. Each IPG may de-tune its receive coil when chargetransfer is complete, independently of the other IPGs, to limit needlesspower loss and undesirable heating within an IPG, without affectingenergy transfer to the remaining charge receiving systems 520, 540, 560.

Moreover, even though a single driver circuit 504 is utilized to driveall three series-connected charge transfer coils 510, 511, 512, thesystem 500 also provides for independent communication with multipleIPGs. Since the forward telemetry (transmit) data signal within the ACsignal is driven across all three series-connected charge transfer coils510, 511, 512, each of the charge receiving systems 520, 540, 560 canindependently receive such a transmitted data signal. As for receivingdata independently from each charge receiving system, the externalcharge transfer system 502 can coordinate the operation of each chargereceiving system 520, 540, 560 so that only one such charge receivingsystem at a time attempts to communicate back telemetry data to theexternal charge transfer system 502. Such coordination may be achievedby forward telemetry commands instructing a selected charge receivingsystem to communicate back telemetry data to the external chargetransfer system 502, so that the non-selected charge receiving systemswill forego attempted back telemetry during such times. Embodimentsdescribed below provide detailed examples of forward and back telemetrycircuitry and operation.

FIG. 11 is a block diagram of a system 600 that provides for thede-tuning of a receive coil within a given IPG to selectively turn offcharge transfer (charge delivery) of the given device without affectingcharge delivery in one or more other such IPGs. Two charge receivingsystems 620, 630 are shown, each disposed within a corresponding IPG. Anexternal charge delivery system 610 disposed outside a dermis layer 602includes series-connected charge transfer coils 612, 613, each of whichcorresponds to a respective one of receive coils 621, 631 of respectivecharge receiving systems 620, 630. In this embodiment, two such chargetransfer coils 612, 613 are shown, one for each charge receiving system620, 630, but other embodiments may utilize one charge transfer coil oranother number of charge transfer coils, depending upon the number ofIPGs.

The external charge transfer system 610 includes a driver 611,responsive to a CTRL signal, for driving the series-connected chargetransfer coils 612, 613 with an AC signal. Within the first IPG, thecharge receiving system 620 includes a receive coil 621 that ispreferably tuned to the resonant frequency of the associated chargetransfer coil 612 within the external charge transfer system 610, sothat receive coil 621 may receive energy transferred from the chargetransfer coil 612 when in close proximity thereto. The receive coil 621is coupled to a rectifier block 622 for receiving energy in a first modeof operation and generating a rectified voltage on node 624, and forde-tuning the receive coil 621 in a second mode of operation, responsiveto a DE-TUNE signal on node 623, to inhibit transfer of energy. Therectified voltage on node 624 is coupled to charge transfer circuitrywithin the first IPG (not shown).

Within the second IPG, the charge receiving system 630 includes areceive coil 631 that is preferably tuned to the resonant frequency ofthe associated charge transfer coil 613 within the external chargetransfer system 610, so that receive coil 631 may receive energytransferred from the charge transfer coil 613 when in close proximitythereto. The receive coil 631 is coupled to a rectifier block 632 forreceiving energy in the first mode of operation and generating arectified voltage on node 634, and for de-tuning the receive coil 631 inthe second mode of operation, responsive to a DE-TUNE signal on node633, to inhibit transfer of energy. The rectified voltage on node 634 iscoupled to charge transfer circuitry within the second IPG (not shown).

Even though a single driver circuit 611 is utilized to drive bothseries-connected charge transfer coils 612, 613, the system 600 providesfor de-tuning of a receive coil within a given IPG to selectively turnoff charging of the given device without affecting charging of one ormore other such IPGs. As such, independent charge transfer of multipleIPGs is provided. When such charge transfer of one of the IPGs iscomplete, the corresponding DE-TUNE signal may be activated within therespective charge receiving system 620, 630 to de-tune its respectivereceive coil 621, 631 and thereby inhibit transfer of energy to therespective charge receiving system 620, 630. Each IPG may de-tune itsreceive coil when charge transfer is complete, independently of theother IPGs, to limit needless power loss and undesirable heating withina fully-charged IPG, without affecting energy transfer to the remainingcharge receiving systems 620, 630. Such completion of charge transfermay be determined within the charge receiving system of the respectiveIPG, with or without any communication to the external charge transfersystem.

FIG. 12 is a block diagram of a system 645 which provides for powertransmission and data communication to an IPG using opposite-polarityhalf-wave rectified signals received by the implanted device. Two chargereceiving systems 650, 660 are shown, each disposed within acorresponding IPG. An external charge transfer system 640 disposedoutside a dermis layer 602 includes series-connected charge transfercoils 642, 643, each of which corresponds to a respective one of receivecoils 651, 661 of respective charge receiving systems 650, 660.Preferably each receive coil 651, 661 is tuned to the resonant frequencyof the respective charge transfer coil 642, 643 within the externalcharge transfer system 640. In this embodiment, two such charge transfercoils 642, 643 are shown, one for each charge receiving system 650, 660,but other embodiments may utilize one charge transfer coil or anothernumber of charge transfer coils.

The external charge transfer system 640 includes a driver 641 that isresponsive to a forward telemetry transmit data signal FWD TELEM TXDATA. When the FWD TELEM TX DATA signal has a first logic state (e.g.,logic high), the driver 641 drives the series-connected charge transfercoils 642, 643 with an AC signal, and when the FWD TELEM TX DATA signalhas a second logic state (e.g., logic low), the driver 641 is disabled.In some embodiments, the driver 641 together with the series-connectedcharge transfer coils 642, 643 may be configured as a resonantamplifier. When such a resonant amplifier is disabled, the AC signal isallowed to decay and eventually cease.

Such operation may be viewed as providing a 100% amplitude-modulated ACsignal driven across the series-connected charge transfer coils 642,643, controlled by a bit-serial forward telemetry data signal FWD TELEMTX DATA. Significant charge transfer to one or both charge receivingsystems 650, 660 is still readily provided for charge transfer bylimiting the duration of time that the forward telemetry transmit datasignal FWD TELEM TX DATA is allowed to “disable” the coil driver 641.Consequently, such a signal also functions as an enable/disable signalfor the driver 641 if maintained in the second logic state.

Within a first IPG, the charge receiving system 650 includes a receivecoil 651 for receiving energy transferred from the associated chargetransfer coil 642 when in close proximity thereto. The receive coil 651is coupled to a positive half-wave rectifier block 653 for receivingenergy and generating a rectified voltage on node 654, and responsive toa DE-TUNE signal on node 655, for de-tuning the receive coil 651 toinhibit transfer of energy from the associated charge transfer coil 642.The rectified voltage on node 654 is coupled to charge transfercircuitry within the first IPG (not shown), which circuitry alsodirectly or indirectly controls the DE-TUNE signal on node 655 whencharging is complete or charge transfer is not desired. The receive coil651 is also coupled via node 657 to a negative half-wave rectifier block652 for receiving forward telemetry data and generating on node 656 arespective forward telemetry receive data signal, which is conveyed toforward telemetry receive data FWD TELEM RX DATA circuitry within thefirst IPG (not shown).

Within a second IPG, the charge receiving system 660 includes a receivecoil 661 for receiving energy transferred from the associated chargetransfer coil 643 when in close proximity thereto. The receive coil 661is coupled to a positive half-wave rectifier block 663 for receivingenergy and generating a rectified voltage on node 664, and responsive toa DE-TUNE signal on node 665, for de-tuning the receive coil 661 toinhibit transfer of energy from the associated charge transfer coil 643.The rectified voltage on node 664 is coupled to charge transfercircuitry within the second IPG (not shown), which circuitry alsodirectly or indirectly controls the DE-TUNE signal on node 665 whencharging is complete or charge transfer is not desired. The receive coil661 is also coupled via node 667 to a negative half-wave rectifier block662 for receiving forward telemetry data and generating on node 666 arespective forward telemetry receive data signal, which is conveyed toforward telemetry receive data FWD TELEM RX DATA circuitry within thefirst IPG (not shown).

As may be appreciated, each IPG can receive forward telemetry dataindependently, irrespective of the charging state (i.e., de-tuned state)of that IPG or of the other IPG. For example, the charge receivingsystem 650 may still receive forward telemetry information by thenegative half-wave rectifier 652 irrespective of whether the positivehalf-wave rectifier 653 is de-tuned or not. Such de-tuning greatlylowers the resonant Q of the combination of charge transfer coil 642 andcharge receive coil 651 for positive voltage excursions on node 657, andconsequently serves to inhibit significant energy transfer to receivecoil 651, but does not negatively impact the ability for the negativehalf-wave rectifier 652 to respond to negative transitions on node 657and generate the output voltage accordingly on node 656. Similarly, thecharge receiving system 650 may still receive forward telemetryinformation irrespective of whether the positive half-wave rectifier 663within the other charge receiving system 660 is de-tuned or not.

FIG. 13A is a block diagram of a system 675 which provides forbi-directional communication with an IPG, and particularly illustratespassive communication from an implanted device to the external chargetransfer system (i.e., back telemetry) when the receive coil within theimplanted device is de-tuned.

Two charge receiving systems 680, 690 are shown, each disposed within acorresponding IPG. An external charge transfer system 670 disposedoutside a dermis layer 602 includes series-connected charge transfercoils 673, 674, each of which corresponds to a respective one of receivecoils 681, 691 of respective charge receiving systems 680, 690. Asbefore, preferably each receive coil 681, 691 is tuned to the resonantfrequency of the respective charge transfer coil 673, 674 within theexternal charge transfer system 670. In this embodiment, two such chargetransfer coils 673, 674 are shown, one for each charge receiving system680, 690, but other embodiments may utilize one charge transfer coil oranother number of charge transfer coils noting that the charge transfercoils are for delivery of charge to the IPGs. Such charge delivery maybe utilized to charge a supercapacitor within the IPG, and/or to powerthe IPG, particularly if such IPG does not include a supercapacitor.

The external charge transfer system 670 includes a driver 671 that isresponsive to a forward telemetry transmit data signal FWD TELEM TXDATA. As described in the embodiment shown in FIG. 12, when the FWDTELEM TX DATA signal is driven to a first logic state (e.g., logichigh), the driver 671 drives the series-connected charge transfer coils673, 674 with an AC signal, and when the FWD TELEM TX DATA signal isdriven to a second logic state (e.g., logic low), the driver 671 isdisabled. In some embodiments, the driver 671 together with theseries-connected charge transfer coils 673, 674 may be configured as aresonant amplifier. When such a resonant amplifier is disabled, the ACsignal decays and eventually ceases. Such operation may be viewed asproviding a 100% amplitude modulation of the AC signal driven onto theseries-connected charge transfer coils 673, 674, which modulation iscontrolled by a bit-serial forward telemetry data signal that alsofunctions as an enable/disable signal for the driver 671 (if held to theappropriate one of its two logic states). The external charge transfersystem 670 also includes a receiver circuit 672 that is responsive tothe AC signal on the series-coupled charge transfer coils 673, 674, andwhich generates accordingly a back telemetry receive data signal BACKTELEM RX DATA.

Within a first IPG, the charge receiving system 680 includes a receivecoil 681 for receiving energy transferred from the associated chargetransfer coil 673 when in close proximity thereto. The receive coil 681is coupled to a positive half-wave rectifier block 683 for receivingenergy and generating a rectified voltage on node 684, and responsive toa DE-TUNE signal on node 685, for de-tuning the receive coil 681 toinhibit transfer of energy from the associated charge transfer coil 673.The rectified voltage on node 684 is coupled to charge transfercircuitry within the first IPG (not shown). The receive coil 681 is alsocoupled via node 687 to a negative peak detector block 682 for receivingforward telemetry data and generating on node 686 a respective forwardtelemetry receive data signal, which is conveyed to forward telemetryreceive data FWD TELEM RX DATA circuitry within the first IPG (notshown).

The charge receiving system 680 also includes a de-tune control block688 for generating the DE-TUNE control signal on node 685 responsive toa disable power transfer signal DISABLE PWR TRANSFER, and furtherresponsive to a bit-serial back telemetry transmit data signal BACKTELEM TX DATA. In operation, the DISABLE PWR TRANSFER signal may beasserted when charge transfer is complete or not desired, which assertsthe DE-TUNE control signal to de-tune the receive coil 681 through thepositive half-wave rectifier 683. In addition, during normal chargetransfer the DE-TUNE control signal may be asserted for eachbit-position of the bit-serial BACK TELEM TX DATA signal correspondingto one of its two data states. Since de-tuning the positive half-waverectifier 683 in concert with the receive coil 681 inhibits energytransfer from the charge transfer coil 673 to the receive coil 681, theloading of charge transfer coil 673 is decreased. This decreased loadingresults in a higher peak current through the series-connected chargetransfer coils 673, 674. In the external charge transfer system 670, thereceiver circuit 672 senses the change in peak current through theseries-coupled charge transfer coils 673, 674 as each serial data bit ofthe BACK TELEM TX DATA signal either tunes or de-tunes the receive coil681, and generates accordingly a back telemetry receive data signal BACKTELEM RX DATA.

If the DE-TUNE control signal is already asserted (e.g., because theDISABLE PWR TRANSFER signal is asserted to indicate charge transfer iscomplete or not desired) when the charge receiving system 680 desires totransmit back telemetry data, the DISABLE PWR TRANSFER signal may bebriefly de-asserted to allow the BACK TELEM TX DATA signal to controlthe DE-TUNE control signal, as is shown in FIG. 13B. Thus, the chargereceiving system 680 may still transmit back telemetry informationirrespective of whether it is generally in a de-tuned state.

Within a second IPG, the charge receiving system 690 includes a receivecoil 691 for receiving energy transferred from the associated chargetransfer coil 674 when in close proximity thereto. The remainder 692 ofthe charge receiving system 690 is identical to the charge receivingsystem 680, and need not be separately described.

FIG. 14A is a block diagram of a system 701 which includes chargetransfer coil (“transmit coil”) current sensing circuitry, andparticularly illustrates sensing such transmit coil current to determineback telemetry data received from an implanted device, and to determinede-tuning of an implanted device receive coil. Two charge receivingsystems 720, 730 are shown, each disposed within a correspondingbody-implanted active device. An external charge transfer system 700disposed outside a dermis layer (or “dermal layer”) 602 includesseries-connected charge transfer coils 703, 704, each of whichcorresponds to a respective one of receive coils 721, 731 of respectivecharge receiving systems 720, 730. Although two such charge transfercoils 703, 704 are shown, one for each charge receiving system 720, 730,other embodiments may utilize one charge transfer coil or another numberof charge transfer coils, depending upon the number of IPGs.

The external charge transfer system 700 includes a driver 702,responsive to a CTRL signal, for driving the series-connected chargetransfer coils 703, 704 with an AC signal. Within the first IPG, thecharge receiving system 720 includes a receive coil 721 that ispreferably tuned to the resonant frequency of the associated chargetransfer coil 703 within the external charge transfer system 700, sothat receive coil 721 may receive energy transferred from the chargetransfer coil 703 when in close proximity thereto. The receive coil 721is coupled to a rectifier/de-tune block 722 for receiving energy attimes and generating a rectified output voltage on node 724, and forde-tuning the receive coil 721 at other times, responsive to arespective BACK TELEM TX DATA signal on node 725, to inhibit transfer ofenergy from the charge transfer coil 703. The rectified voltage on node724 is coupled to charge transfer circuitry within the first IPG (notshown). In this embodiment the BACK TELEM TX DATA signal functions asboth a bit-serial data signal and a “disable charge transfer” signal,much like the DE-TUNE signal in the previous embodiment. In order tode-tune the receive coil 721 and disable charge transfer, the BACK TELEMTX DATA signal is driven and held in one of its two logic levels (e.g.,a logic high level), while to actually communicate back telemetry datato the external charge transfer system 700, the BACK TELEM TX DATAsignal is driven between both its logic levels according to the bitserial data. Any of several encoding formats may be used, but NRZ(“non-return-to-zero”) encoding is assumed here.

Within the second IPG, the charge receiving system 730 includes areceive coil 731 that is preferably tuned to the resonant frequency ofthe associated charge transfer coil 704 within the external chargetransfer system 700, so that receive coil 731 may receive energytransferred from the charge transfer coil 704 when in close proximitythereto. The receive coil 731 is coupled to a rectifier/de-tune block732 for receiving energy at times and generating a rectified outputvoltage on node 734, and for de-tuning the receive coil 731 at othertimes, responsive to a respective BACK TELEM TX DATA signal on node 735,to inhibit transfer of energy from the charge transfer coil 704. Therectified voltage on node 734 is coupled to charge transfer circuitrywithin the second IPG (not shown).

The external charge transfer system 700 includes circuitry to generate aCOIL CURRENT signal corresponding to the magnitude of the chargetransfer coil current, and to generate a BACK TELEM RX DATA signalcorresponding to the back telemetry data received from one of the chargereceiving systems 720, 730. The back telemetry data is communicatedpassively by a given one of the charge receiving systems 720, 730 bymodulating the amount of energy transferred from the external chargetransfer coils and received by a given charge receiving system. Suchmodulation occurs by changing whether the corresponding receive coil istuned or de-tuned. De-tuning the receive coil may occur when chargetransfer is complete or not desired, in which case the transferredenergy will decrease and remain at the decreased value, but may alsooccur in response to a bit-serial BACK TELEM TX DATA signal, in whichcase the variations or changes in transferred energy will have afrequency component matching the bit rate of the BACK TELEM TX DATAsignal. The back telemetry data is received by the external chargetransfer system by sensing the variation in charge transfer coil currentthat corresponds to changes in the amount of energy transferred to thegiven charge receiving system.

In this embodiment, the circuitry to accomplish this includes a chargetransfer coil AC current sensor 706 having an input coupled to theoutput node 705 of driver 702, which generates on its output node 707 anAC voltage signal corresponding to the instantaneous current through theseries-connected charge transfer coils 703, 704. This AC voltage signalon node 707 is coupled to a demodulator 708 which generates on itsoutput node 709 a demodulated signal corresponding to the peak value ofthe AC voltage signal on node 707, which corresponds to the peak valueof the instantaneous current through the charge transfer coils 703, 704.This demodulated signal on node 709 is filtered by low-pass filter 710to generate the COIL CURRENT signal on node 712. The COIL CURRENT signalis a generally DC-like signal that is reflective of the low-frequencychanges in the peak charge transfer coil current, such as would occurwhen charge transfer is no longer desired and its corresponding receivecoil is de-tuned and remains de-tuned for some time.

The demodulated signal on node 709 is also coupled to a band-pass filter711 to generate the BACK TELEM RX DATA signal on node 713. This BACKTELEM RX DATA signal is reflective of higher-frequency changes in thepeak charge transfer coil current, such as would occur when backtelemetry data is being communicated and the corresponding receive coilis de-tuned and tuned responsive to the bit-serial BACK TELEM TX DATAsignal. Illustrative waveforms of these signals are shown in FIG. 14B.In some embodiments the data rate for the back telemetry need not beidentical to the data rate for the forward telemetry. For example, theback telemetry data rate, relative to the resonant frequency of thecharge transfer coils in the external charge transfer system, may beresult in each bit interval (i.e. bit position) corresponding to as fewas 20 cycles of the resonant amplifier, as noted in FIG. 14B. Additionalexamples and other embodiments of such current sensing and receive datacircuits are described below.

As noted above, FIG. 14B shows waveforms of selected signalsillustrating back telemetry operation in the embodiment shown in FIG.14A. In particular, the bit-serial BACK TELEM TX DATA signal (node 725)is shown representing several bits of information to be communicatedfrom the charge receiving system 720 to the external charge transfersystem 700, along with the corresponding tuned or de-tuned status of thereceive coil 721. The peak current through the charge transfer coil 703is higher corresponding to the de-tuned state of the receive coil 721. Avoltage signal is generated at the output 707 of the current sensor 706,which voltage signal corresponds to the instantaneous current throughthe charge transfer coil 703. This output signal 707 is demodulated toproduce the demodulated output signal on node 709, which is thenfiltered by band-pass filter 711 to produce the BACK TELEM RX DATAsignal on node 713.

FIG. 15 is a block diagram of an exemplary charge transfer system 745which provides for adjustable transmitted power to improve powerefficiency within an implanted device. Two charge receiving systems 620,630 are shown, each disposed within a corresponding IPG, which areidentical to those described in FIG. 11, and need not be described here.An external charge transfer system 740 disposed outside a dermis layer602 includes series-connected charge transfer coils 612, 613, each ofwhich corresponds to a respective one of receive coils 621, 631 ofrespective charge receiving systems 620, 630. Two such charge transfercoils 612, 613 are shown, one for each charge receiving system 620, 630,but other embodiments may utilize one charge transfer coil or anothernumber of charge transfer coils, depending upon the number of IPGs.

The external charge transfer system 740 includes a resonant driver 743for driving the series-connected charge transfer coils 612, 613 with anAC signal, and a buck/boost circuit 741 that provides on node 742 avariable DC voltage for use by the driver 743 as an upper power supplynode. By varying this VBOOST voltage on node 742, the amount of energystored each resonant cycle in the charge transfer coils and ultimatelytransferred to the corresponding receive coil may be varied, forexample, to achieve better charge delivery efficiency and couplingwithin the implanted device. The resonant driver 743 is responsive to aCTRL signal, such as described above regarding other embodiments, whichmay function as both a data signal and as an enable signal.

The VBOOST voltage on node 742 may be varied as charge transferprogresses (or the charge delivery requirements change) within each IPG.For example, during an early phase of charge transfer when the voltageis relatively low, it may be desirable to limit the rectified voltage onnode 624 so that any voltage drop across the charge transfer circuitwithin the IPG is kept to a minimum necessary to achieve proper voltageregulation, or to provide a particular constant magnitude of chargetransfer current to efficiently charge the supercapacitor. Later, ascharge transfer progresses and the delivered voltage is raised to ahigher voltage, the rectified voltage on node 624 may be increased tomaintain a desired voltage drop across such charge transfer circuitry orto maintain the desired charge transfer current. When one of the IPGs isfully charged and its receive coil (e.g., 621) is de-tuned, the otherIPG may still be transferring charge and its receive coil (e.g., 631)still tuned for resonant energy transfer from the external chargesystem. The VBOOST voltage may then be adjusted to optimize the amountof energy transfer into the remaining IPG.

The buck/boost circuit 741 is shown as being responsive to an ADJUSTCTRL signal, which may be controlled within the external charge transfersystem in response to detecting a decrease in energy transfer to one ormore IPGs (e.g., using the COIL CURRENT signal described above), byreceiving back telemetry information from one or both IPGs regardinginternal voltage levels, internal current levels, and/or internaltemperatures, or by one or more temperature sensors within the externalcharge transfer system (e.g., a sensor placed near each charge transfercoil), or by any other useful means, such as information from one orboth IPGs conveyed using a Bluetooth connection to the external chargetransfer system. This adjustability of the VBOOST voltage provides foradjustable control of the energy coupled to one or both of the chargereceiving systems within the IPGs, even though both series-connectedcharge transfer coils 612, 613 are driven by a single driver circuit743. However, it should be noted that changing of the amount of energythat can be coupled to any of the IPGs will change the amount of energytransfer to all the IPGs. Thus, although not disclosed herein, the IPGsmust operate such that charge delivered is governed by the one of theIPGs that requires the most charge transfer. Each of the IPGs, forexample, will send information back to the external charge deliverysystem in the form of a request to indicate an increased need for chargeand the amount of charge transfer will be increased until the IPGrequiring the most charge has that request satisfied.

FIG. 16A is a block diagram of an exemplary system 780 which includesfeedback excitation control of a resonant coil driver amplifier. Twocharge receiving systems 620, 630 are shown, each disposed within acorresponding IPG, which are identical to those described in FIG. 11,and need not be described here. An external charge transfer system 770disposed outside a dermis layer 602 includes series-connected chargetransfer coils 773, 774, each of which corresponds to a respective oneof receive coils 621, 631 of respective charge receiving systems 620,630. While two such charge transfer coils 773, 774 are shown, one foreach charge receiving system 620, 630, other embodiments may utilize onecharge transfer coil or another number of charge transfer coils,depending upon the number of IPGs.

The external charge transfer system 770 includes a resonant driver 771for driving the series-connected charge transfer coils 773, 774 with anAC signal. An adjustable VBOOST voltage is conveyed on node 742 toprovide a variable DC voltage for use by the driver 771 as an upperpower supply node. The resonant driver 771 is responsive to a CTRLsignal, such as described above, which may enable/disable the driver 771when appropriate (e.g., after charge transfer is complete within bothIPGs), and may also convey forward telemetry information to one or bothIPGs, both as described above. The external charge transfer system 770also includes a coil current trigger circuit 772 for generating on node776 a TRIGGER signal conveyed to the resonant driver 771 to provide aperiodic “excitation” signal to periodically pump additional energy intothe resonant driver 771, which is helpful to maintain a high degree ofefficiency of the resonant operation of the driver 771 in concert withthe series-connected charge transfer coils 773, 774 connected to theoutput node 775 of the resonant driver 771. The coil current triggercircuit 772 preferably is configured to assert the TRIGGER signal whenthe instantaneous charge transfer coil current, during each resonantcycle, crosses a predetermined threshold that is proportional to thepeak instantaneous charge transfer coil current. In other words, whenthe instantaneous charge transfer coil current crosses a value that is apredetermined percentage of the maximum current (e.g., 60% of peakcurrent), the TRIGGER signal is asserted to pump the additional energyinto the resonant amplifier (i.e., driver 771 and transmit coils 773,774). Illustrative waveforms of the instantaneous charge transfer coilcurrent and the TRIGGER signal are shown in FIG. 16B.

By generating a feedback-controlled TRIGGER signal in this manner, highefficiency resonant operation may be achieved even as the chargetransfer coil current may vary. Such variation in charge transfer coilcurrent may result from changes in the VBOOST voltage, from changes intransferred energy due to receive coil de-tuning within an associatedcharge receiving system, from forward telemetry which modulates thecharge transfer coil (i.e., “transmit coil”) current, from variations incomponent parameters, and from changes in voltage, temperature, or otherenvironmental conditions.

M. Headset Charge Transfer System

FIG. 17 is a block diagram of an exemplary headset 781 that includes anexternal charge transfer system for two head-located IPGs, such as twoimplantable pulse generator (IPG) devices. The headset includes an IPGDriver and Telemetry block 782 that drives two charge transfer coils783, 784, and which is powered by a battery voltage VBAT conveyed onnode 785 by headset battery 788, and an adjustable voltage VBOOSTconveyed on node 786. A buck/boost circuit 787 receives the VBAT voltageon node 785 and generates the VBOOST voltage on node 786. Power transferis provided by a Headset Battery Charger 789 which receives USB powerfrom USB port 791. A VDD regulator 790 also receives the VBAT voltage onnode 785 and generates a VDD voltage (e.g., regulated to 3.0 volts) onnode 794, which is generally used as a power supply voltage for certaincircuitry within the headset.

A microcontroller (MCU) 793 provides general configuration control andintelligence for the headset 781, and communicates with the IPG Driverand Telemetry block 782 via a forward telemetry signal FWD TELEM and aback telemetry signal BACK TELEM via a pair of data lines 796. The MCU793 can also communicate with an external device (e.g., a smartphone orpersonal digital assistant (PDA), a controller, a diagnostic tester, aprogrammer) that is connected to the USB port 791 via a pair of USB datalines 792. The MCU 793 is connected to an external crystal resonant tankcircuit 797 for providing an accurate timing source to coordinate itsvarious circuitry and data communication interfaces. A Bluetoothinterface 795 provides wireless interface capability to an externaldevice, such as a smartphone or other host controller, and is connectedto the VDD voltage on node 794. The Bluetooth interface 795 communicateswith the MCU 793 using data/control signals 798. In general, MCU 793 isutilized to store configuration information in an on-chip Flash memoryfor both the overall headset and charge transfer system and also provideconfiguration information that can be transferred to one or more of theIPGs. The overall operation of the headset is that of a state machine,wherein the IPG driver/telemetry block 782 and the other surroundingcircuitry, such as the buck/boost circuit 787 and the headset batterycharger 789, all function as state machines, typically implementedwithin an ASIC. Thus, when communication information is received thatrequires the MCU 793 to transfer configuration information to the IPGor, alternatively, to configure the headset state machine, the MCU 793will be activated. In this embodiment a state machine is utilized formost functionality because it has a lower power operation, whereas aninstruction-based processor, such as the MCU 793, requires more power.It should be understood, however, that such a headset can utilize anytype of processor, state machine or combinatorial logic device.

FIG. 18, which includes FIGS. 18A and 18B, is a schematic diagram of anexemplary IPG driver and IPG telemetry circuit, such as the IPG Driverand Telemetry block 782 shown in FIG. 17. While these FIGS. 18A and 18Beach represent a portion of the complete FIG. 18 and may be arrangednext to each other (aligned at the dotted line on each figure) to viewthe entire FIG. 18, the portion shown on FIG. 18A may be generallyreferred to as the IPG driver circuit, even though certain portions ofthe IPG driver circuit is shown in FIG. 18B, and the portion shown onFIG. 18B may be generally referred to as the IPG telemetry circuit, eventhough certain portions of the IPG telemetry circuit is shown in FIG.18A.

Referring now to the complete FIG. 18, a portion of a charge transfersystem is depicted which includes a coil driver 161 for a pair ofseries-connected charge transfer coils 151, 152, and a driver controlcircuit 162 for the coil driver 161. The coil driver 161 together withthe charge transfer coils 151, 152 may be viewed as a resonant amplifiercircuit 163. The driver control circuit 162 provides a control signal onnode 114 that serves to turn off the coil driver 161 at times, and toperiodically cause energy to be pumped into the resonant amplifier 163at other times, as will be explained below.

The coil driver 161 may be understood by looking first at excitationcoil 144 and driver transistor 133. In resonant operation, the drivertransistor 133 is periodically turned on, which drives the voltage ofnode 134 to ground (labeled 130). Since the excitation coil 144 isconnected between node 786, which conveys a VBOOST voltage, and node134, which is now grounded by transistor 133, the VBOOST voltage isimpressed across the excitation coil 144 and consequently a currentflows through the excitation coil 144, which current stores energy inthe excitation coil 144. The magnitude of the VBOOST voltage may bevaried (e.g., between 1.0 and 5.5 volts) to vary the amount of energystored in the excitation coil 144 per cycle, to thus vary the amount ofenergy coupled to the receive coils (also referred to as “secondarycoils”). Capacitor 145 provides local filtering for the VBOOST voltageconveyed on node 786. When the driver transistor 133 is then turned off,the energy in excitation coil 144 is “pumped” into the LC resonantcircuit formed by parallel-connected capacitors 141, 142, 143 connectedin series with the charge transfer coils 151, 152. Resistor 153represents the parasitic resistance of the charge transfer coils 151,152 and their associated wiring. Illustrative waveforms are shown inFIGS. 19A, 19B, and 19C. In certain embodiments, the resonant frequencyis preferably on the order of 750 kHz.

Three separate capacitors 141, 142, 143 are used to distribute the peakcurrent that would otherwise flow through the leads, solder joints, andstructure of a single capacitor, to instead achieve a lower peak currentthrough each of capacitors 141, 142, 143. But in understanding theoperation of this circuit, these three capacitors 141, 142, 143 may beviewed as effectively providing a single resonant capacitor. When drivertransistor 133 is turned on, it is desirable to drive node 134 to avoltage as close to ground as possible, to reduce losses that wouldotherwise result from a large drain-to-source current and a non-zerodrain-to-source voltage across driver transistor 133. Consequently, thedrain terminal of driver transistor 133 is connected by several distinctpackage pins to node 134.

Driver transistor 133 is controlled by the output 131 of buffer 125,which is coupled to the gate of driver transistor 133 through resistor132. The buffer 125 is connected to operate as an inverting buffer sincethe non-inverting input IN (pin 4) is connected to VCC (pin 6), and theinverting input INB (pin 2) is utilized as the buffer input that isconnected to node 114, which is the control signal generated by drivercontrol circuit 162. Thus, when node 114 is low, the output node 131 ofbuffer 125 is high, and driver transistor 133 is turned on. The outputnode 131 is coupled to the gate of driver transistor 133 throughresistor 132 to limit the peak current charging and discharging the gateterminal of driver transistor 133, and to also provide (together withthe parasitic gate capacitance of driver transistor 133) an RC filterfor the signal actually coupled to the gate terminal of drivertransistor 133.

As mentioned above, when driver transistor 133 is turned on, it isdesirable for node 134 to be driven to a voltage as close to ground aspossible. To help achieve this, it may be likewise desirable to drivethe gate terminal of driver transistor 133 to a voltage higher than thebattery voltage VBAT conveyed on node 785. To accomplish this, a localpower circuit including diodes 127, 129, 136, 137, and capacitors 128,138, may be utilized.

During circuit startup, the buffer circuit 125 operates with its “VCCvoltage” (conveyed on local power node 126) essentially at the batteryvoltage VBAT, less a small diode drop through diode 129. The VBATvoltage may be 3.5-4.0 volts, which is sufficient to operate the buffer125 to provide adequate output voltage levels on node 131 tosufficiently turn on/off driver transistor 133 to initiate and maintainresonant operation. In such resonant operation, driver transistor 133 ispreferably turned off at a particular time in each resonant cycle topump energy into the resonant circuit, as will be explained furtherbelow. Each time that the driver transistor 133 is turned off, thevoltage on node 134 rises quickly as the current through excitation coil144 continues to flow into node 134. This rising voltage is coupledthrough capacitor 138 onto node 139, through diode 136, and onto thelocal power node 126 for buffer 125. The magnitude of thepositive-transition of the voltage on node 134 results in a voltage onlocal power node 126 that may be as high as 8.0 volts, which is higherthan the VBAT voltage, especially when operating in the lower range ofbattery voltage (e.g., as the battery discharges). When the voltage oflocal power node 126 rises above the VBAT voltage, diode 129 preventsany back-current into the VBAT node 785, and Zener diode 127 operates tolimit, for safety reasons, the maximum voltage developed on local powernode 126. Capacitor 128 provides local filtering on the local power node126 irrespective of whether the buffer 125 is powered by the battery(through diode 129) or by resonant operation of the coil driver circuit161 (through diode 136).

The driver control circuit 162 generates on output node 114 a drivercontrol signal that controls when driver transistor 133 is turnedon/off. In resonant operation, the driver control signal 114 ispreferably a periodic signal that causes the driver transistor 133 toturn off at a predetermined time during each resonant cycle, and to turnback on at a later time during each resonant cycle, to thereby causeenergy to be pumped into the resonant amplifier 163 during each resonantcycle. In addition, at certain times the driver control signal 114 ispreferably driven high to cause the driver transistor 133 to turn offand remain off for a time duration longer than a resonant cycle, whichprevents energy from being pumped into the resonant amplifier, and thusallows the resonant amplifier operation to decay and eventually cease.

The driver control circuit 162 includes a Schmitt-trigger NAND gate 108having a local power supply node 112 (also labeled 4VF) which is coupledto the battery voltage VBAT using a small noise-isolation resistor 120and a local filter capacitor 113. An input circuit includes capacitor107, diode 110, and resistor 111, which together generate a first inputsignal on node 109 (NAND input pin 2) responsive to a TRIGGER signalconveyed on node 106. A feedback circuit includes diode 122, resistors118, 119, and capacitor 105, which together generate a second inputsignal on node 104 (NAND input pin 1) responsive to the driver controlsignal generated on the output node 114.

To understand operation of the driver control circuit 162 during normaloperation of the resonant amplifier circuit 163, assume that the TRIGGERsignal 106 is high, both inputs of NAND 108 (nodes 104, 109) are high,and the output of NAND 108 (driver control signal 114) is low.Consequently, node 131 is high (due to inverting buffer 125) and drivertransistor 133 is turned on, driving node 134 to ground and causingcurrent to flow from VBOOST (node 786) through the excitation coil 144to ground.

As will be explained in detail below, the TRIGGER signal on node 106 isthen driven low, thus creating a falling-edge (i.e., negativetransition) on the voltage of node 106. Capacitor 107 couples thisnegative transition to node 109, which is coupled to a voltage below thelower input threshold of Schmitt NAND gate 108. As a result, the outputnode 114 is driven high, node 131 is driven low, and transistor 133 isturned off. This happens almost immediately after the falling edge ofthe TRIGGER signal 106.

With the TRIGGER signal 106 still low, the resistor 111 will charge node109 until its voltage reaches the upper input threshold of Schmitt NANDgate 108, at which time the NAND gate 108 output node 114 is againdriven back low, node 131 is driven high, and transistor 133 is turnedon. The values of resistor 111 and capacitor 107 are chosen, in concertwith the upper and lower input thresholds of the Schmitt NAND gate 108,to determine the output high pulse width of output node 114, and thusdetermine the length of time that transistor 133 is turned off.

When the TRIGGER signal 106 is driven back high, this positivetransition is coupled by capacitor 107 to node 109, but the coupledcharge is snubbed by diode 110 to prevent an excessive positive voltagethat would otherwise be generated at node 109, and instead maintain thevoltage of node 109 at essentially the VBAT voltage.

If there are no transitions of the TRIGGER signal 106, the voltage ofnode 109 (NAND input pin 2) remains high, and the feedback circuit(diode 122, resistors 118, 119, and capacitor 105) causes the outputnode 114 to oscillate. This occurs because the voltage of node 104 (NANDinput pin 1) slowly follows the voltage of the output node 114 due tothe RC circuit formed by the feedback resistors 118, 119 (and diode 122)coupled between the output node 114 and input node 104, and thecapacitor 105 coupled to node 104 itself. Diode 122 is included so thatthe parallel combination of resistors 118, 119 charges node 104 after apositive-going output transition, while only resistor 119 dischargesnode 104 after a negative-going output transition. This asymmetry helpskeep node 104 nominally very close to the VBAT level during normalresonant operation, to essentially disable the “watchdog timer” aspectof this circuit as long as periodic TRIGGER signals are received.

The component values of resistors 118, 119 and capacitor 105 arepreferably chosen so that the self-oscillation frequency of node 114 ismuch lower than the resonant frequency of operation (and likewise theexpected frequency of the TRIGGER signal 106 during resonant operation,as will be explained in greater detail below). In some embodiments theself-oscillation frequency is approximately 3-4 times lower than theresonant frequency. This self-oscillation provides a suitable periodicconduction path through driver transistor 133 to initiate operation ofthe resonant amplifier 163 until the TRIGGER signal 106 is generated percycle, which provides for more efficient operation and greater spectralpurity of the resonant amplifier circuit 163. Resistors 116 and resistor117 form a voltage divider to generate on node 115 an IPG_CHRG_FREQsignal reflective of the actual charger frequency.

A forward telemetry data signal FWDTELEM conveyed on node 101 is coupledto the gate terminal of NMOS transistor 103, which terminal is coupledto ground 130 by biasing resistor 102. The operation described thus-farabove assumes that the FWDTELEM signal remains at ground, and thustransistor 103 remains turned off. If the FWDTELEM signal is drivenhigh, NAND gate 108 input node 104 is driven to ground, which causes theNAND gate 108 output node 114 to be driven high, irrespective of thesecond NAND input node 109. This, of course, turns off driver transistor133 for as long a time as FWDTELEM remains high, and causes resonantoperation of the resonant amplifier circuit 163 to decay and eventually,if disabled for a long enough time, to cease entirely. Then, when theFWDTELEM signal is driven back low and transistor 103 turns off, thedriver control circuit 162 begins to self-oscillate, thus startingoperation of the resonant amplifier circuit 163 and the eventualgeneration of the TRIGGER signal 106 to more precisely control thetiming of driver transistor 133. Such resonant “lock-in” occurs fairlyquickly, usually in only 1-2 cycles. In some embodiments, the resonantfrequency is approximately 750 kHz, and the forward data rate isapproximately 10 kHz (i.e., a 100 μS bit interval), and the timerequired for the resonant amplifier 163 to decay (when FWDTELEM isdriven high), and to re-start and lock-in resonant operation (whenFWDTELEM is driven low), is a small portion of an individual bitinterval. A more detailed description of such forward data transmission,including receiving such transmitted data in a charge receiving system,follows below.

As described above, in normal resonant operation the negative transitionof the TRIGGER signal 106 determines when the driver transistor 133 isturned off during each resonant cycle of the amplifier circuit 163, andthe RC input circuit on node 109 determines how long the drivertransistor 133 remains off. Preferably the driver transistor 133 has a30% duty cycle (i.e., turned off 30% of the time). In thisimplementation, feedback circuitry shown in FIG. 18B is utilized thatgenerally tracks the actual current through the charge transfer coils151, 153, and generates the negative-going transition of the TRIGGERsignal 106 at a time during each resonant cycle when the increasinginstantaneous charge transfer coil current exceeds a predeterminedpercentage of the peak current through the charge transfer coils 151,152. Careful selection of the predetermined percentage improves theefficiency of resonant amplifier operation and reduces unwanted harmoniccomponents of the oscillation frequency.

The generation of the TRIGGER signal 106 begins with acurrent-to-voltage converter circuit 260 formed by the series-connectedresistors 203, 204 and capacitor 206 coupled between the HV node 140(the same node driving the series-connected charge transfer coils 151,152) and ground 130. Resistor 205 is a biasing resistor. With properselection of component values, the instantaneous voltage generated atnode 202 will be proportional to the instantaneous current through thecharge transfer coils 151, 152. Such may be achieved by proper selectionof the resistor and capacitor values in the current-to-voltage convertercircuit 260 to achieve the same time constant as the inductor andparasitic resistor values in the charge transfer coils. Specifically,the values are preferably chosen so that R/C=L/R. Referencing the actualcomponents, this relationship is then (R₂₀₃+R₂₀₄)/C₂₀₆=(L₁₅₁+L₁₅₂)/Rp₁₅₃(e.g., where R₂₀₃ means the value of resistor 203). If this relationshipis followed, the instantaneous voltage at node 202 is an AC voltage thatis proportional to (i.e., corresponds to) the instantaneous AC currentthrough the charge transfer coils 151, 152. Normally, this AC voltage onnode 202 would be symmetric and centered around the ground voltage, asshown in FIG. 19A, but in this embodiment the AC voltage on node 202 isoffset to a non-negative voltage range by a ground restore circuit 261.

The ground restore circuit 261 includes an amplifier 207 having a localpower supply node 201 (also labeled 4VH) which is coupled to the batteryvoltage VBAT (conveyed on node 785) using a small noise-isolationresistor 209 and a local filter capacitor 208. The amplifier 207non-inverting input (pin 3) is coupled to ground, and the invertinginput (pin 2) is coupled to node 202. A feedback circuit includescapacitor 210, resistor 211, and diode 212. In operation, this groundrestore circuit 261 translates the AC voltage signal on node 202 to anon-negative voltage signal of the same magnitude, whose peak lowvoltage is ground, and whose peak high voltage is twice that otherwisegenerated on node 202 in the absence of the ground restore circuit 261.This resulting waveform for node 202 is shown in FIG. 19A. The peakvoltage at node 202 may be 2-3 V.

The signal on node 202 is coupled to a demodulator circuit 262 thatincludes amplifier 213, diode 215, resistors 217, 219, and capacitors218, 220. Node 202 is coupled to the non-inverting input (pin 5) ofamplifier 213. The inverting input (pin 6) of amplifier 213 is coupledto the output node 214 to achieve operation as a voltage follower. Diode215 and capacitor 218 generate on node 216 a voltage corresponding tothe peak voltage driven onto node 214 by amplifier 213 (less a smallvoltage drop through diode 215), and bleeder resistor 217 reduces thevoltage on node 216 if the peak voltage on node 214 assumes a lowervalue corresponding to a decrease in the current through the chargetransfer coils 151, 152. Such a situation will be more fully describedbelow in the context of back telemetry. Lastly, the peak voltage on node216 is RC-filtered by resistor 219 and capacitor 220 to generate on node257 a signal having less ripple than the signal on node 216. This signalon node 257 is then buffered by the buffer 263 which includes anamplifier 221 (also configured as a voltage follower) to generate onnode 222 a more robust signal representing the magnitude of the peakcurrent through the charge transfer coils 151, 152. Resistors 230, 233and filter capacitor 231 generate a TELEM_CURRENT signal on node 232having a scaled magnitude relative to the peak charge transfer coilcurrent represented by node 222. In this implementation, with preferredvalues of the resistors 230, 233 values, the TELEM_CURRENT signal has amagnitude that is one-half the magnitude of the peak charge transfercoil current.

Comparator 228 is configured to essentially “compare” the instantaneouscharge transfer coil current against a percentage of the peak chargetransfer coil current, and generate the falling-edge on the TRIGGERsignal 106 during each cycle of resonant operation when the rising edgeof the instantaneous charge transfer coil current rises above apredetermined percentage of the peak charge transfer coil current.

The voltage signal on node 202 corresponds to the instantaneous chargetransfer coil current, which is coupled through resistor 227 to theinverting input of comparator 228. The peak charge transfer coil currentsignal on node 222 is divided by a resistor divider formed by resistors225, 223 to generate on node 226 a reference signal representing apredetermined percentage of the peak charge transfer coil current.Capacitor 224 provides local filtering to stabilize this signal on node226, which is coupled to the non-inverting input of comparator 228. Whenthe inverting input of comparator 228 rises above the non-invertinginput, the output signal TRIGGER on node 106 is driven low, as isdepicted in FIG. 19A.

The “peak charge transfer coil current” signal on node 222 varies as oneor more secondary coils is de-tuned, such as would occur to indicatethat charging is complete (if such de-tuning occurs continuously) or tocommunicate back telemetry data from one of the IPGs (if such de-tuningis performed corresponding to a bit-serial data stream). TheTELEM_CURRENT signal on node 232 is preferably configured to correspondto slowly changing values of the peak charge transfer coil current,while the remaining circuitry to the right of amplifier 221 is utilizedto detect more frequent (i.e., higher frequency) changes in the chargetransfer coil current, as would occur during back telemetry of data fromone of the IPGs.

The buffer 263 output signal on node 222 is AC-coupled through capacitor234 to node 246, which is nominally biased by resistors 235, 236 atone-half the 4VH voltage on node 201, which essentially is the VBATvoltage on node 785. Thus, node 246 has a nominal DC bias equal toVBAT/2, upon which is superimposed an AC signal corresponding to changesin the magnitude of the peak charge transfer coil current. This node 246is coupled to an input of a band-pass filter/amplifier 264, whichincludes an amplifier 237, resistors 239, 241 and capacitors 240, 248.Specifically, node 246 is coupled to the non-inverting input ofamplifier 237. Feedback resistor 239 and capacitor 240 are each coupledbetween the output node 238 of amplifier 237 and the inverting inputnode 247 of amplifier 237.

The band-pass filter/amplifier 264 generates on its output node 238 ananalog signal representing received data. This analog data signal iscoupled through resistor 242 to generate an analog “back telemetry”signal BKTELEM_ANA. The band-pass filter/amplifier 264 also generates onnode 245 a reference signal corresponding generally to the mid-point ofthe transitions of the analog data signal on node 238, which is the samebias level (e.g., VBAT/2) as node 246. This signal is coupled throughresistor 256 to generate a reference “back telemetry” signalBKTELEM_REF. Both the BKTELEM_ANA and BKTELEM_REF signals may beconveyed to control circuitry (not shown) and may be used as diagnostictest points.

The gain of the band-pass filter/amplifier 264 is determined by thevalue of resistor 239 divided by the value of resistor 241. In certainpreferred implementations, the gain may be equal to 10. The value ofcapacitor 240 is selected to provide the desired high frequency rolloff,and the value of capacitor 248 is selected to provide the desired lowfrequency rolloff.

The analog data signal on node 238 and the analog reference signal onnode 245 are coupled to a comparator circuit 265 to generate on itsoutput node 250 a digital signal representing the back telemetry datasignal. The comparator circuit 265 includes a comparator 249 having alocal (4VG) power supply node 254 which is coupled to the batteryvoltage VBAT (conveyed on node 785) using a small noise-isolationresistor 253 and a local filter capacitor 255. In this implementation,the comparator circuit 265 is preferably configured to provide a voltagegain of 27, which is determined by the input resistor 243 connectedbetween node 238 (i.e., the output node of the band-passfilter/amplifier circuit 264) and the non-inverting input node 244 ofcomparator 249, and the feedback resistor 252 connected between theoutput node 250 of comparator 249 and the non-inverting input node 244of comparator 249. The voltage of this non-inverting input node 244 iscompared to the data reference voltage coupled to the inverting inputnode 245 of comparator 249 to generate on output node 250 the digitalsignal representing the back telemetry data signal. This digital signalis coupled through resistor 258 to generate on node 251 a digital backtelemetry data signal BKTELEM_DIG.

FIG. 20 is a schematic diagram of an exemplary headset buck/boostcircuit, such as the buck/boost circuit 787 shown in FIG. 17. In thisembodiment, the buck/boost circuit utilizes a commercially availablehigh efficiency single-inductor buck-boost converter circuit 369, suchas the TPS36020 from Texas Instruments, Inc. The VBAT voltage conveyedon node 785 is coupled to an input filter circuit that includescapacitor 351, ferrite bead 352, and capacitors 354, 355, whose outputon node 353 is coupled to a pair of voltage input pins VIN1, VIN2 of theconverter circuit 369. A single inductor 371 is coupled between a firstpair of connection pins L1, L2 (node 370) and a second pair ofconnection pins L3, L4 (node 372). The output of converter circuit 369is provided on a pair output pins VOUT1, VOUT2, which are coupled vianode 367 to an output filter circuit that includes capacitors 374, 375,376 and ferrite bead 380, to provide the VBOOST voltage on node 786. Aprecision resistor divider 377, 378 provides a monitoring voltageBOOST_MON on node 379.

A boost enable input signal BOOST_EN is coupled via node 359 to anenable input EN of the converter circuit 369, and also coupled to anRC-filter circuit formed by resistor 357 and capacitor 356, whose outputon node 358 is coupled to a VINA pin (supply voltage for the controlstage) and SYNC pin (enable/disable power save mode; clock signal forsynchronization) of the converter circuit 369. The converter outputvoltage on node 366 is coupled to a voltage divider circuit thatincludes resistors 373, 365 to generate on node 366 a feedback voltagewhich is coupled to the FB input of the converter circuit 369. A boostPC input signal BOOST_PC is coupled via node 360 to a voltage divideradjustment circuit that includes resistors 361, 363 and capacitor 364,each coupled to node 362, and whose output is coupled to node 366. Inthis manner the BOOST_PC signal can essentially alter the voltagedivider ratio to adjust the output voltage of the converter 369 and thusalter the VBOOST voltage.

As noted above, FIGS. 19A, 19B, and 19C illustrate voltage waveforms ofselected signals depicted in the embodiment shown in FIG. 18, and alsoseveral signals depicted in FIG. 23A. FIG. 19A generally illustrateswaveforms related to sensing the charge transfer coil current andgenerating the TRIGGER signal accordingly. The various waveforms showthe charge transfer coil current, the I-to-V Converter 260 output signalon node 202 without the effect of the ground restore circuit 261, theI-to-V Converter 260 output signal on node 202 with the effect of theground restore circuit 261, the demodulator node 257, the reference node226 (shown having a value equal to 60% of the peak voltage on node 257),and the resulting TRIGGER signal on node 106. The left half of thefigure corresponds to a lower magnitude of charge transfer coil current,and the right half of the figure corresponds to a higher magnitude ofcharge transfer coil current.

FIG. 19B generally illustrates waveforms related to the driver control162 and the resonant amplifier 163. Shown are the TRIGGER signal on node106, the resulting waveform on NAND 108 input 2 (node 109), the NAND 108input 1 (node 104), the resulting waveforms on the NAND 108 output node114, and the buffer 125 output node 131, the resulting voltage on thedrain terminal of transistor 133 (node 134), and the current through thecharge transfer coils 151, 152. The resonant oscillation frequency inthis exemplary embodiment corresponds to an oscillation period of about1.33 microseconds.

FIG. 19C generally illustrates waveforms related to forward telemetryoperation. The upper waveform illustrates the FWDTELEM signal on node101 conveying a serial bit stream data signal conveying several bits ofinformation, with each bit interval, for this exemplary embodiment,being about 100 microseconds long. When the FWDTELEM signal is drivenhigh at transition 322, the NAND 108 input 1 (node 104) is driven toground, as shown in the second waveform, to disable the charge transfercoil driver 161. As a result, the previously oscillating signal on thegate node 131 of transistor 133 is likewise driven to ground, as shownin the third waveform, which disables the resonant amplifier 163 andcauses the charge transfer coil 151, 152 current to decay and eventuallycease, as shown in the fourth waveform. The fifth and sixth waveformsare described below in detail with regard to FIG. 22A, and illustratethe current in the receive coil 402 likewise decays and ceases,resulting in a corresponding signal on the negative peak detector outputnode 410, and a resulting falling transition 323 on the FWD TELEM RXDATA signal on node 419. An additional logical inversion of this signalmay be easily accomplished to generate a data signal having the samepolarity as the FWDTELEM signal.

When the FWDTELEM signal is driven low at transition 324, the NAND 108input 1 (node 104) charges back to a high level, which allows the drivercontrol 162 to again oscillate, initially controlled by its own feedback“watchdog timer” operation, and later under control of the TRIGGERsignal. As a result, the gate node 131 of transistor 133 again exhibitsan oscillating signal causing transistor 133 to periodically “pump” theresonant amplifier 163, and the charge transfer coil 151, 152 once againoscillates, as shown in the fourth waveform. As described below indetail with regard to FIG. 22A, the current in the receive coil 402 isinduced because of the charge transfer coil current, resulting in acorresponding signal on the negative peak detector output node 410, anda resulting rising transition 325 on the FWD TELEM RX DATA signal onnode 419.

N. Implantable Pulse Generator

FIG. 21 is a block diagram of an exemplary body-implantable activedevice 400, such as an implantable pulse generator (IPG) device. Areceive coil 402 (also referred to as a secondary coil 402) is connectedto a RECTIFIER block 401 that generates a PWRIN signal on node 408 andan RFIN signal on node 414. Both the PWRIN signal on node 408 and theRFIN signal on node 414 are connected to a TELEMETRY/DE-TUNE block 451that receives a forward telemetry signal on the RFIN node 414, and whichinteracts with the PWRIN node 408 to de-tune the receive coil 402 tothereby communicate back telemetry information and/or disable furtherenergy transfer to the receive coil 402. The PWRIN node 408 is alsoconnected to a POWER/CHARGE TRANSFER block 453 that is responsible forgenerating one or more internal voltages for circuitry of thebody-implantable device 400, and for transferring charge to asupercapacitor 532 and for providing charge to the electrode of one ormore electrodes 533.

A microcontroller (MCU) 457 provides overall configuration andcommunication functionality and communicates forward and back telemetryinformation via a pair of data lines 419, 425 coupled to the TELEMETRYblock 451. Data line 419 conveys a forward telemetry RX signal, and dataline 425 conveys a back telemetry TX signal. The MCU 457 receivesinformation from and provides configuration information to/from thePOWER/CHARGE TRANSFER block 453 via control signals PWR CTRL conveyed oncontrol lines 452. A programmable electrode control and driver block 454(DRIVERS 454) generates electrical stimulation signals on each of agroup of individual electrodes 455. An adjustable voltage generatorcircuit BOOST 458, which is coupled via signals VSUPPLY (node 430), SW(node 433), and VBOOST DRV (node 438) to components external to the ASIC450 (including capacitor 431, inductor 432, and rectifier block 437)provides a power supply voltage VSTIM to the DRIVERS block 454.

The MCU 457 provides configuration information to the DRIVERS block 454via configuration signals CONFIGURATION DATA conveyed on configurationlines 456. In some embodiments, the POWER/CHARGE TRANSFER block 453, theTELEMETRY block 451, the BOOST circuit 458, and the DRIVERS block 454are all implemented in a single application specific integrated circuit(ASIC) 450, although such is not required. In the overall operation, theASIC 450 functions as a state machine that operates independently of theMCU 457. The MCU 457 includes Flash memory for storing configurationdata from the external control system (not shown) to allow a user todownload configuration data to the MCU 457. The MCU 457 then transfersthis configuration data to ASIC 450 in order to configure the statemachine therein. In this manner, the MCU 457 does not have to operate togenerate the driving signals on the electrodes 455. This reduces thepower requirements. Other embodiments may implement these threefunctional blocks using a combination of multiple ASIC's, off-the-shelfintegrated circuits, and discrete components.

Charge transfer is monitored by the ASIC 450 and adjusted to provide themost efficient charge transfer conditions and limit unnecessary powerdissipation to provide a constant current to the supercapacitor 532 andelectrodes 533. Preferable conditions for charging the supercapacitorinclude a charging voltage of approximately 4.5 V for most efficientenergy transfer (with a minimum charge voltage of about 4.0 V). Also, itis particularly desirable to maintain a constant charge transfer currentinto the supercapacitor in a charging charge transfer operation duringthe entire charge transfer time, even as the battery voltage increasesas it charges. Preferably this constant charge transfer current is aboutC/2, which means a charging current that is one-half the value of thetheoretical current draw under which the supercapacitor would deliverits nominal rated capacity in one hour. To accomplish this, a variety ofsensors and monitors (not shown) may be included within thebody-implantable device 400 to measure power levels, voltages (includingthe battery voltage itself), charge transfer current, and one or moreinternal temperatures.

As a further description of the overall operation of the IPG, thegeneral operation is that of a state machine utilizing the ASIC 450. Ingeneral, the MCU 457 is utilized as an instruction based processor forcommunication and configuration operations. The state machine 450 ismore efficient in carrying out a simple repetitive program, onceconfigured and initiated. Thus, in operation, the state machine or ASIC450 is normally running the stimulation program and controlling thecurrent to the lead 535 and the various electronic connections 455.During the operation of the state machine, however, there are certaintimes when information has to be transmitted back to the headset inorder to change, for example, the transmittal power level. As notedhereinabove, it is important to minimize the amount of power that istransmitted across the dermis to the coil 402 in order to minimizeheating. Thus, it is important to keep the voltage level on the node 408as low as possible while maintaining the system in constant currentregulation. Current regulation is monitored and, when the system goesout of current regulation due to the input voltage 408 falling, arequest is sent back to the headset to increase the power transferred.This requires the state machine 450 to wake up the MCU 457 to effect thecommunication. Once current regulation is achieved, it is then notnecessary to have the MCU operating and it will be placed into a “sleep”mode of operation. Whenever configuration information is required to besent to the IPG from the headset, the headset then sends a request tothe IPG, which wakes up the MCU 457. The MCU 457 then services thisrequest and downloads configuration information to the internal Flashmemory, a nonvolatile memory. The configuration is stored in the MCU 457and then the MCU 457 uploads the configuration data to the ASIC 450.Thus, the MCU 457 is basically utilized for the communication operationwith the headset and also as a repository for configuration informationfor the ASIC 450.

Referring now to FIG. 22A, there is illustrated a five block diagram ofthe IPG. As noted hereinabove, there is provided overall state machine460 to control the operation of the system to control drivers to providea constant current level to electrodes on any one of multiple leads 535or 536. The driver 454 is provided current through a current controlledregulator 459. The power level is adjusted via communication with theheadset to adjust the power transferred to the coil 402 vary the voltageout of the rectifier block 401. This current controlled regulator 459 iscontrolled to both charge and maintain charge on the supercapacitor 532and also provide current to the driver 454. Once the supercapacitor 532is charged, and the current required by the driver 454 is more than canbe provided by the supercapacitor 532, the driver 454 receives all ofthe power from the headset across the coil 402. As long as the voltagelevel on the node 408 is at a sufficient level to maintain currentregulation in the regulator 459, current can be provided at theappropriate regulated level. However, if the voltage level increases atnode 408, heat will be dissipated in the regulator 459 unnecessarily.Therefore, communication is maintained with the headset to minimize theamount of power transferred to lower the voltage on node 408 to a pointthat is high enough to maintain current regulation but no higher. Thus,when the voltage required to drive the coil on the headset side islowered, the regulator 459 falls out of regulation, at which time, therequest will be sent back to the headset to increase the power in orderto just maintain the necessary voltage on node 408 to maintain currentregulation for a particular neurostimulation program being run.

Referring now to FIG. 22B, there is illustrated a flowchart depictingthe overall operation of running a program, which is initiated at aStart block 802. The program then flows to a decision block 804 todetermine if a program has been initiated on the IPG to providestimulation to the individual. If so, this will then require theelectrodes to be driven with a constant current. Until a program isinitiated, the process goes to block 806, where the amount of powerrequired to maintain the IPG in a low power mode is minimal. This can befacilitated by maintaining the supercapacitor 532 in a chargeconfiguration. The supercapacitor 532 is a type of capacitor thatfunctions as a battery in that it will maintain a small, charge theirown for short duration of time. When the system is initially turned on,there will be no power to the unit and the supercapacitor 532 must becharged from a zero value. Thus, the system is placed into an initialPower Up mode of operation to power on the MCU 457 and the ASIC 450, atwhich time the current is limited to the supercapacitor 532. Once poweris at a sufficient level to power the MCU 457, charge will be deliveredto the supercapacitor 532, but this will be delivered at a maximumcurrent level to ensure that the amount of charge transfer crossed thedermis to the coil 402 is minimize to reduce heating. Once thesupercapacitor 532 is charged, then the system will go into a normaloperating mode and, if there is no stimulation program that is requiredto be run at that time, MCU 457 will put into a sleep mode and the coil402 detuned to eliminate power transfer thereto, such that all powerprovided in the sleep mode is provided by the supercapacitor 532. As thecharge falls on the supercapacitor 532, the coil 402 will be tuned toallow power to be transferred to the IPG from the headset. This willmaintain the supercapacitor 532 in a charged state. In the event thatthe headset is removed, and tuning of the coil 402 in order to allowcharge to be transferred results in no charge being transferred, thisindicates a possible powerdown mode. All compliments we placed in theirlowest power mode to ensure that the supercapacitor 532 can maintain theIPG in a low power sleep mode for as long as possible. Since allconfiguration data for the ASIC 450 is stored in the MCU 457, it is notnecessary to modify the configuration data, as it can always be uploadedback to the ASIC 450 in the power of mode. The supercapacitor 532 isprovided to allow the IPG to be maintained in a low power mode for ashort duration of time. If, for example, the IPG were in the middle of astimulation program, delivering current to the electrodes, and theheadset were removed, then the ASIC 450 would terminate the program toprevent additional current from being drawn from the supercapacitor 532.

Once the program is initiated, the program will flow to a function block808. This will result in constant current being delivered to the selectelectrodes on the lead 535 by the drivers 454 in accordance with thestimulation program. The stimulation program could activate certainelectrodes on the lead, define certain electrodes as cathodes or anodesor isolate certain electrodes and also define the amount of current thatis the being delivered to a particular electrode, the waveform that isbeen being delivered thereto, etc. The program then flows to a decisionblock 810 in order to determine if the current is at a defined currentthreshold. If the current is below current threshold, i.e., the amountof power being delivered necessary to maintain current regulation, ASICwill recognize that the current regulator has fallen out of regulationand move to function block 814, where the MCU 457 will affect a transmitof a request to raise the power at the headset in order to increasepower transfer to the coil 402. It may be that other IPGs have sent arequest to lower power, but each IPG will independently request a higherpower to maintain current regulation for its drivers. If, however, thecurrent is not below the threshold, the process moves to block 812,where the MCU 457 will transmit a request to the headset to lower theheadset power and power transfer. In some embodiments, function block812 is optional, and the headset may, on its own, lower the power if,after a certain period of time, none of the IPGs have requestedincreased power. The headset will lower the power only if there is norequest to increase power from other IPGs. This, of course, may resultin a higher power than is necessary for the input of the currentregulator at the requesting IPG, but it is only important that the IPGrequiring the most power transfer be serviced by the headset and thepower transfer maximized for that IPG. As soon as an IPG goes into asleep mode, it will no longer send requests for power level increases ordecreases and the headset will recognize this and periodically decreasethe power. If the power goes too low for a particular IPG, then that IPGwill indicate to the headset that the power needs to be increased at theheadset and the power transfer increased. Once current regulation isestablished, the program flows to a decision block 816 to determine ifthe neurostimulation program at the IPG has been terminated. If so, theprogram flows to a Return block 818 and, if not, the program flows alonga “N” block back to the input of the function block 808.

FIG. 23A is a schematic diagram of an exemplary RECTIFIER block 401 andTELEMETRY/DE-TUNE block 451, both such as those shown in FIG. 21. Theexemplary RECTIFIER block 401 includes a resonant half-wave rectifiercircuit 421 and a half-wave data rectifier circuit 422. The resonanthalf-wave rectifier circuit 421 may be viewed as an “energy receivingcircuit” and the half-wave data rectifier circuit 422 may be viewed as a“data receiving circuit.” The exemplary TELEMETRY/DE-TUNE block 451includes a current mirror circuit 420, and a de-tuning transistor 424.

The circuitry depicted in FIG. 23A may be viewed as a portion of acharge receiving system which includes a secondary coil 402, an energyreceiving circuit (421), and a data receiving circuit (422). Theresonant rectifier circuit 421 includes diode 405, capacitor 404, andcapacitor 407, which, together with the secondary coil 402, operates asa resonant half-wave rectifier circuit. When the secondary coil 402 isdisposed in proximity to its associated charge transfer coil, such asone of the charge transfer coils 151, 152 (see FIG. 18), during a timewhen the resonant amplifier 163 is operating, the charge transfer coiland the secondary coil may be inductively coupled and may have, withcareful design of the coils and reasonably close physical proximity, a Qthat approaches 100. Consequently, the resonant amplifier circuit 163and the resonant rectifier circuit 421 will operate as a resonant ClassE DC-to-DC voltage converter. During such operation, energy is coupledto the secondary coil 402 due to magnetic induction.

This induced energy in secondary coil 402 is manifested as a sinusoidalvoltage on node 403 that traverses above and below the ground referencelevel on node 440. This AC voltage on node 403 is half-wave rectified toprovide a DC voltage on node 408 that may be used to provide power toboth operate and/or charge the supercapacitor (if present) within theIPG. Specifically, because a single diode 405 is used in this circuit,and due to the polarity of this diode, only the positive voltagetransitions on node 403 are rectified, thus creating a positive DCvoltage on node 408. A zener diode 406 is coupled between node 408 andground to prevent an excessive positive voltage from being generated atnode 408.

The above description of the resonant rectifier circuit 421 and itshalf-wave rectifier circuit operation has assumed that transistor 424remains off. This ensures that the Q of the combined primary chargetransfer coil 151 and the secondary coil 402 remains high, and energy isefficiently transferred. However, if transistor 424 is turned on (whenthe DE-TUNE/BACK TX DATA signal on node 425 is high), the secondary coil402 is “de-tuned” which significantly reduces the Q of the resonantcircuit, and thereby reduces charge transfer and thus reduces coupledpower into the secondary coil 402. This may be useful at times to reducepower, such as when the supercapacitor has been fully charged or when nocharge delivery is required. It is also useful to turn on transistor 424to communicate back telemetry information to the charge transfer system.Analogous back telemetry operation is described above in reference toFIGS. 14A and 18, and corresponding waveforms are shown in FIGS. 14B and19A.

The data receiving circuit 422 includes diode 409, capacitor 411, andresistor 412, which together may be viewed as a negative half-waverectifier circuit or negative peak-detector circuit. Irrespective ofwhether the de-tune transistor 424 is active, the generated voltage onnode 410 corresponds to the peak negative voltage of the sinusoidalvoltage signal on node 403. If the peak negative voltage increases inmagnitude (i.e., becomes more negative) over multiple cycles, the diode409 will quickly drive node 410 to a correspondingly more negativevoltage, and capacitor 411 serves to maintain this voltage. Conversely,if the peak negative voltage decreases in magnitude (i.e., becomes lessnegative) over multiple cycles, the resistor 412 will drive node 410 toa correspondingly less negative voltage. The value of resistor 412 andcapacitor 411 may be chosen to provide a response time that isconsistent with forward telemetry data rates. Exemplary forwardtelemetry data rates may be on the order of 10 kHz.

The data receiving circuit 422 together with the current mirror circuit420 generates on node 419 a signal FWD TELEM RX DATA reflecting theforward telemetry received data. The current mirror 420 is powered by aVDD voltage conveyed on node 417, and generates a reference currentthrough resistor 413 and P-channel transistor 415, which is mirrored byP-channel transistor 416 to generate a current through resistor 418which generates a corresponding voltage signal on node 419. Dependingupon the current gain of the current mirror 420, node 419 may be eitherdriven virtually all the way to the VDD voltage (less a V_(DSSAT)voltage of transistor 416), or may be pulled by resistor 418 well towardground, to generate a “quasi-digital” forward telemetry receive datasignal. Additional digital regeneration circuitry (e.g., within theASIC, and not shown) may be employed to create a truly digital datasignal.

FIG. 23B generally illustrates voltage waveforms of selected signalsdepicted in the embodiment shown in FIG. 23A. In particular, waveformsare shown for the induced voltage at node 403 (one end of the receivecoil 402), the DE-TUNE gate signal on node 425, the PWRIN signal on node408, the negative peak detector signal on node 410, and the currentmirror output node 419. The left portion 471 corresponds to the receivecoil 402 being “tuned” to transfer charge, the right portion 472corresponds to the receive coil 402 being “de-tuned” to inhibit chargetransfer, in response to the transition 473 of the DE-TUNE gate signalto a high level, as shown in the second waveform. This high voltagelevel turns on transistor 424, which grounds node PWRIN, as shown in thethird waveform, and likewise “clamps” the voltage on node 403 to a smallpositive voltage 474 due to diode 405, while not affecting the negativeinduced voltage 475 on node 403, and similarly without affecting thenegative peak detector voltage on node 410 and the voltage on currentmirror output node 419.

The rightmost portion 476 of the figure shows the induced voltage inreceive coil decaying when the resonant amplifier in the external chargetransfer system is disabled. This could occur because the externalcharge transfer system turned off its resonant amplifier in response todetecting a long term de-tuning of the receive coil in thebody-implantable active device (i.e., when charge transfer is no longerdesired). This could also occur in response to a back telemetrycommunication calling for charge transfer to cease. This could alsooccur merely because another bit of forward telemetry information iscommunicated. In any of such possible situations, the resonant amplifier163 is disabled, which allows the resonant operation (and AC currentthrough the charge transfer coils) to decay, and as a result the inducednegative voltage at node 403 of the receive coil likewise decays, asshown by waveforms 477. This causes a corresponding decay in the voltageof negative peak detector node 410, and an eventual change of state 478of the current mirror output node 419.

FIG. 24 is a schematic diagram of portions of an adjustable voltagegenerator circuit, such as the adjustable voltage generator circuitBOOST 458 shown in FIG. 22, and particularly highlights the externalcomponents to the ASIC 450, in accordance with some embodiments of theinvention. In this embodiment, a VSUPPLY voltage generated within theASIC 450 and conveyed on node 430 is coupled to filter capacitor 431 andinductor 432. The other end of the inductor 432 is coupled via node 433to the drain terminal of switch transistor 439 within the ASIC 450,which is controlled by a BOOST CTRL signal connected to its gateterminal. A pair of diodes 434, 435 and capacitor 436 together form arectifier block 437 and serve to rectify the SW signal voltage on node433 and thus generate the VBOOST DRV voltage on output node 438.

FIG. 25 is a diagram representing a headset 580 that includes anexternal charge transfer system 581 for two separate body-implantabledevices, each implanted behind a patient's respective left and rightears. Each of the body-implantable devices may be a head-locatedneurostimulator system, such as that described below. The chargetransfer system 581 is connected to a pair of headset coils 582, 592 byrespective wire pairs 583, 593. When the headset 580 is worn by apatient, the headset coils 582, 592 (charge transfer coils) are placedin proximity to the corresponding receive coil 584, 594 in eachrespective IPG.

The exemplary headset 580 includes an IPGS driver, telemetry circuit, amicrocontroller (MCU), a battery, and a Bluetooth wireless interface.The headset 580 may also communicate with a smartphone or PDA 596, formonitoring and/or programming operation of the two head-locatedneurostimulator systems.

FIG. 26 depicts two implanted IPGs with leads to cover both sides of thehead. Prominent here are Fronto-Parietal Lead (FPL) 20 b and OccipitalLead (OL) 30 b, which lie within the subcutaneous layer 82. The twostructures are numbered identically with respect to their compliments,and they are implanted identically, one on the left side of the head andone on the right side of the head, as described above. Also illustratedis zygomaticotemporal nerve 62 and the supratrochlear nerve 72.

FIG. 27 depicts one implanted IPG with leads to cover both sides of thehead. In this embodiment, the FPL 20 b extends from the IPG 10 a on oneside of the head around the parietal region on that side of the head,the two frontal regions and on the parietal region on the opposite sideof the head such that there are two PEAs 26, two FEAs 25 and two OEAs35. This, of course, requires an incision to be made on the temporalregion on the side of the head on which the IPG 10 is implanted and afrontal incision made to allow the FPA 20 to be routed to and in afrontal incision and then to a temporal incision on the upside the headand finally to the parietal region on the upside the head. This is thesame with respect to the occipital lead 30 that must be routed throughpossibly an additional acetylene incision of the back of the head. Allthat is required is the ability to route particular leads to therespective regions proximate the nerves associated therewith. This willallow a single IPG 10 to cover two frontal regions, two parietal regionsand two occipital regions.

The exemplary headset 580 includes an IPG driver, telemetry circuitry, amicrocontroller (MCU), a battery, and a Bluetooth wireless interface.The headset 580 may also communicate with a smartphone or PDA 596, formonitoring and/or programming operation of the two head-locatedneurostimulator systems.

O. First Embodiment

The first embodiment provides for a system that incorporates one or moreof the features outlined above and includes a head-mounted,radiofrequency coupled, unibody neurostimulating system comprising anIPG 10 and at least two neurostimulating leads (FPL 20 and OL 30). Thesystem may be implanted in a manner such that the IPG 10 and two leads20, 30 are disposed as illustrated in FIG. 5, FIG. 6, FIG. 7 and FIG. 9.The IPG 10 is capable of, via a radiofrequency couple, functionallyconnecting to and communicating with an ECU 100, which houses a powersupply, as well as electronic components that provide for diagnosticsand programming functionality.

In this embodiment, the leads are constructed as described above and asdepicted in the drawings. The FPL 20 is approximately 26 cm in lengthfrom its proximal end 22 to its distal end 21. The FPL 20 has a distalnon-stimulating tip of approximately 3 mm in length that abuts the FEA,which may have ten SME 24 uniformly disposed over approximately 8 cm.This is followed by an inter-array interval 27 of approximately 4 cm,then the PEA, which may include eight SME 24 uniformly disposed overapproximately 6 cm, and finally a proximal lead segment 22 a that endsat the proximal end 22, where the lead transitions to the IPG 10 and thelead internal wires 29, 38 connect to the ASIC 13.

In this embodiment, the occipital lead may comprise a plastic bodymember 39 over which six SME 34 may be disposed uniformly overapproximately a 10 cm length of the lead, and the lead terminates inapproximately a 3 mm distal non-stimulating tip 33.

In this embodiment, the IPG 10 comprises the elements described aboveand depicted in the drawings, including an ASIC 13, an internal magnet12, and an internal radiofrequency receiver coil 11, which all may behoused in a medical grade metal can with plastic cover 14. In thisembodiment the dimensions of the IPG 10 measured along the outer surfaceof the plastic cover 14 may be approximately 5 cm by 3 cm by 0.5 mm.

This is more fully illustrated in FIG. 3A the implantable pulsegenerator 10. The ASIC 13 is comprised of multiple chips disposed on asubstrate or supporting PC board 13′. The coil 11 and the magnet 12 aredisposed on a similar PC board 11′ for support thereof. They areconnected together by connecting wires 12′ for providing power betweenthe coil 11 and the ASIC 13. If the coil 11 is disposed in the distallydisposed body 10′, the wires in 12′ are run through the lead 20′illustrated in FIG. 1B. On the opposite end of the PC board 13′ from thewire connection 12′, there are provided a bundle of wires 29, associatedwith the FPL 20, for example, although the wires 38 associated with theOL 30 are not illustrated. This bundle of wires runs through theproximal end of the lead 20. The plastic cover 14 is comprised of amedical grade plastic, formal coating that covers the entire surface ofboth the coil 11 and the associated structures and ASIC 13. The magnet12, although not shown, can be disposed within an open well within thecover 14 to allow removal thereof. This is typically done whenever apatient is subjected to an MM, requiring the removal of the magnet andreinsertion of it at a later time. The cover 14 extends downward alongthe lead 20 to provide a seal therewith and a distal end 24′. Thisprovides a unibody construction, such that the proximal ends of theleads 29 are attached to the PC board 13′ during manufacture and thenthe coating 14 applied thereto.

Turning to FIGS. 8 and 9, the system includes an ECU 100, whichfunctionally couples to the IPG by a radiofrequency couple mechanism.The purpose of the ECU 100 is to provide power to the implanted unit, aswell as programming and diagnostic functionality.

In this embodiment, the system is capable of handling a program from theECU 100 that includes such parameters as pulse amplitude, frequency andpulse width.

In this embodiment, the ECU 100 is positioned “behind the ear” and heldin place by an ear clip 1110. The ECU's EBC 1120 contains the mainelectronics and battery, along with the necessary circuits, theelectrical output of which is channeled via the external RF coil lead1130 to the external RF coil 1141, which is held in place over thecorresponding internal RF receiver coil 11 by external and internalmagnets 1142, 12. By an RF coupling mechanism, the ECU 100 is capable ofproviding power, as well as overall unit control, including programmingand diagnostic functionality.

P. Alternate Embodiments

There are multiple alternate embodiments that preserve the features ofthe neurostimulation system disclosed herein, which include variationsin the dimensions of the fronto-parietal and occipital leads which,along with their respective surface metal electrode arrays, extend tocover multiple regions of the head. In various embodiments, the spacingand dimensions of the electrode array(s) may be constant, or theelectrode arrays may be specifically designed with respect to electrodetype, dimensions, and layout for improving the therapeuticeffectiveness.

Other embodiments may include variations in the design of the externalcontrol unit. For example, instead of securing to the head via an earclip mechanism, it may secure through an “ear muffs” type of mechanism.

Other embodiments may include variations in the design and location ofthe internal RF coil and internal magnet with respect to the location ofthe IPG proper. In our primary embodiment here, the IPG is disclosed ashaving two lobes—one for the ASIC and the other for the internal RFreceiver coil and magnet. In one example of an alternate embodiment, theIPG may be provided as a single lobe, which houses the ASIC, internal RFreceiver, and internal magnet together.

In another example of an alternate embodiment, the internal RFcoil/magnet may be located some distance from the leads and IPG properand be functionally connected by an extended lead containing internalconnecting wires. This embodiment would allow for the RF coil/magnetcomponent to be located at various locations in the head, neck andtorso.

Thus, the disclosure comprises extended electrode array designs (two ormore regions by a single lead), and/or multiple arrays and optimizedintra-array electrode dispositions. The disclosure also comprises leadconfigurations, which include the capability of a modular lead designthat provides for ports on either the standard FPL or OLs. In anotherembodiment, the IPG receive additional separate leads, if and asnecessary either at the time of initial implant or in the future.

Further, the lead lengths, along with the specific technical makeup anddimensions of the individual surface metal electrodes and electrodearrays, may be varied to include more or less than three unilateralregions of the head (occipital, parietal, and frontal) contemplated bythe first embodiment. For example, a single IPG may energize and controlmultiple additional leads of varying lengths that ultimately could bedisposed over virtually every region of the head and face bilaterally.

At least two electrodes may be included per region, and while the firstembodiment calls for a total of 24 electrodes disposed over three arrayscovering three different regions of the head—the occipital, parietal andfrontal regions—there is no absolute limit to the maxim number ofelectrodes. Similarly, while the first embodiment calls for threeelectrode arrays, the disclosure contemplates two, or even one, array(so long as the array covers at least two regions). There is also nolimiting maximum for the number of arrays. Also, there may be multiplevariations of design within each separate array, including for example,variations in the number, dimensions, shape, and metal composition ofthe individual electrodes, as well as the distance and constancy ofdistance between electrodes, within each array. Further, each array mayhave the same or completely different designs.

While the neurostimulation system has been described for implantation asa peripheral neurostimulator in the head and for head pain, it iscapable of being implanted and used as a peripheral nerve stimulatorover other regions of the head and face than described above and alsoover other peripheral nerves in the body.

Certain embodiments may incorporate an adjustable voltage generationcircuit (e.g., a buck/boost circuit as shown in FIG. 17 and FIG. 20)that utilizes a local power supply voltage, such as a battery voltage,to generate a VBOOST voltage that is typically higher in voltage thanthe local power supply. However, the VBOOST voltage in certainembodiments may be higher or lower than the local power supply voltage,depending upon the battery voltage, the desired energy transfer to thebody-implanted active devices, and other factors.

Q. Operation

When functioning, the implanted neurostimulator is functionallyconnected to the ECU by an RF couple, the internal circuit of leadinternal wires is connected to an IPG, and the SME of the various arraysare programmed to function as anodes and cathodes. The generatedelectrical pulse wave then passes from the ASIC of the IPG to theassociated internal lead wire and ultimately to its associated terminalsurface metal electrode. The current then passes a short distance fromthe subcutaneous tissue to a contiguous, or nearby, electrode, wherebyit passes back up the lead to its associated proximal metal contact, andthen back to the IPG to complete the circuit. The generated pulse wavespass through the subcutaneous tissue between two terminal electrodes andstimulate the sensory nerves of the area. When active, the IPG may beprogrammed to produce continuous series of pulse waves of specifiedfrequency, amplitude, and pulse width. It is this series of pulse wavesactively stimulating a patient's locally associated nerves thatunderpins the therapeutic effect of the implanted unit. The electricalpulse wave then passes from a connected proximal surface metal contact,along the associated internal lead wire, and ultimately to itsassociated terminal surface metal contact.

Referring now to FIG. 28, there is illustrated a headset 1902 disposedabout the cranium for interfacing with the two implants 10 a of FIG. 26.The headset 1902 includes right and left coupling coil enclosures 1904and 1906, respectively that contain coils coupled to the respectivecoils in the implants 10 a. The coil enclosures 1904 and 1906 interfacewith a main charger/processor body 1908 which contains processorcircuitry and batteries for both charging the internal battery in theimplants 10 a and also communicating with the implants 10 a. Thus, inoperation, when a patient desires to charge their implants 10 a, allthat is necessary is to place the headset 1902 about the cranium withthe coil enclosures 1904 and 1906 in close proximity to the respectiveimplants 10 a. This will automatically effect charging.

Referring now to FIG. 29, there is illustrated a diagrammatic view ofthe power regulation system at the IPG. As noted hereinabove, theoriginal rectified voltage is the “raw” voltage that is received fromthe headset via the inductive coupling. This is provided on the node408. As noted hereinabove also, this drives the current regulator 459,which is operable to output a regulated current on a node 2902. This isoperable to drive the supercapacitor 532, with the voltage noted asV_(BAT) for the overall storage voltage, it being understood that thesupercapacitor 532 could be replaced with a regular battery. The currentregulator 459 is a logic circuit that will operate on any voltage. Thus,when the voltage is input thereto and rises above a predeterminedthreshold voltage above which the regulator 459 will maintain currentregulation, the current provided to the node 2902 will be regulated at,in an exemplary disclosed embodiment, 30 mA. This is utilized to chargethe supercapacitor 532 and to minimize the maximum output current thatcan be sinked to the supercapacitor 532. The reason for this is tominimize the amount of power delivered through the inductive coupling tothe IPG. If there were no limit on the amount of current, then thesupercapacitor would be charged at a very high rate initially until itreached its maximum charge at the voltage applied. Thus, the currentregulator 459 is operable to charge the supercapacitor 532 up to itsmaximum charge level, which will be the maximum voltage applied on thenode 2902. As will be described hereinbelow, the voltage on the node408, the induced voltage, V_(INDUCED), will be maintained at a levelthat will be sufficiently above the voltage on the node 2902 to maintaincurrent regulation. This is typically a voltage of 1.0 Volts, but thisdepends upon the design of the current regulator 459. There is alsoprovided a resister 2904 disposed in series between the node 2902 andthe upper plate of the supercapacitor 532. This is an alternativecurrent sensing resistor which has a very small value of, for example,0.1 ohms. By measuring the voltage across this resistor 2904, ameasurement of the current delivered directly to the supercapacitor 532can be determined. Additionally, there are provided to sensing lines2906 and 2908 for measuring the voltage across the current regulator459. With knowledge of the voltage drop across the current regulator 459required to maintain regulation, it would then be possible to maintainthe voltage on the node 408 slightly at or above that voltage in orderto maintain current regulation. Of course, as the supercapacitor 532charges, the voltage will increase, requiring the voltage on the node408 to be increased.

The CPU 457 and the current driver 454 (the current driver beingrealized with current DACs) are logic circuits that required a fixedoperating voltage, below which they will not operate. Thus, there isprovided a linear regulator 2910 which is operable to provide anoperating voltage, V_(DD), for operating all of the logic circuit andthe current driver 454 in the ASIC. When the voltage falls below V_(DD),the logic associated with the circuits will not operate and that theywill be placed into some type of hibernating or sleep mode. When thevoltage on the supercapacitor 532 rises above the level that allows thelinear regulator 2910 to regulate the voltage to V_(DD), the CPU 457will go into a Power Up Reset mode of operation and initiate theoperation of the IPG to run the programmed stimulation. Onceoperational, it will also be able to communicate with the headset viathe transceiver 451.

During operation, the CPU 457 is operable to determine the variousvoltages associated with the current sensing operation. The minimum thatis required is to sense the voltage on the lines 2906 and 2908. Thesevoltages are input to ADCs 2914 to provide a digital voltage for the CPU457 to encode and transferred to the headset. As noted above, theresistor 2904 could be an alternate current sensing element thatmeasures the direct current to the supercapacitor 532. Additionally, itis desirable to sense the current to the current DACs 454 both to theanodes via a sensing resistor 2920 and from the cathodes via a sensingresistor 2922. Each of these has an associated set of sensing lines thatare input to an associated one of the ADCs 2914. Thus, the CPU 457 canprovide to the headset voltage information regarding the voltage dropacross the current regulator 459, the voltage drop across the sensingresistor 2904, the voltage drop across the sensing resistor 2920 and thevoltage drop across the sensing resistor 2922.

In operation, the supercapacitor 532 is charged up and provides thenecessary driving current to the rest of the circuit during operation.During operation of the IPG and driving of the electrodes E₁-E_(\N) toprovide the stimulation to the associated nerves, current is drawn offof the supercapacitor 532 by the logic circuitry associated with the CPU457 and the ASIC and also by the driving current required to drive theelectrodes. The maximum current for this is approximately 3.0 mA.Depending upon the size of the supercapacitor 532, there will be afinite time within which the supercapacitor 532 will require additionalcharge to be provided by the current regular 459. Initially, uponconnection of a headset, the supercapacitor 532 might have an operationwhere it is desirable to quickly charge the supercapacitor 532 to themaximum voltage. After this initial charge, required in order to get theIPG up and running quickly, any replenishment of this charge might notrequire 30 mA of charge but, rather, a lower charge rate. This lowercharge rate could be affected by pulsing in the induced voltage orhaving a current regulator with a lower voltage drop associatedtherewith. Thus, a variable current current regulator 459 could beimplemented. The whole purpose is to reduce the amount of voltage on thenode 408 to the minimum amount required for the overall operation toreduce any heating at the inductive coupled point across the skin.

Referring now to FIG. 30, there is illustrated a diagrammatic view ofthe voltage during charging. Initially, when the supercapacitor 532 isdischarged below the required voltage for the linear regulator 2910, theIPG will be powered down. This is represented by a voltage 3002. Inorder to increase his voltage, the induced voltage from the headset mustbe at least, in one example, 1.0 Volts above the voltage of node 2902.This will allow 30 mA of current to flow through the current rightregulator 459. Thus, if the headset were intelligent enough to provide atime to increase to follow charging pattern of the supercapacitor 532,it would follow a dotted line 3004. However, the headset does not haveknowledge of this. Thus, a predetermined voltage, V_(INIT), will beapplied as the induced voltage 408. This would be a voltage that wasknown to be above required to operate the linear regulator 2910.However, it should be understood that the voltage required by a headsetin order to have an induced voltage at a particular level can beaffected by multiple factors such as the positioning of the headsetrelative to the IPG, the particular manner by which the IPG wasimplanted in a particular patient, etc. Thus, the voltage can initiallybe increased well above the worst-case to scenario. This will allow thevoltage on the node 2904 to increase from the voltage 3002 up to avoltage at a point 3006 that represents the point at which the linearregulator 2910 will provide operating voltage to CPU 457. At this point,voltages across the current regulator 459 or any of the sensingresistors 2904, 2924 2922, can be transmitted to the headset. Theheadset can then decrease the voltage or increase the voltage toinfluence the voltage on the node 408 to maintain that induced voltageas low as possible in order to maintain current regulation on thecurrent regulator 459. This will continue until the supercapacitor 532is fully charged, at a point 3008. There can be some hysteresisprogrammed into the operation of the headset such that the voltage onthe supercapacitor 532, i.e., the voltage on the node 2902, will have todecrease by a predetermined percentage before additional charging willbe effected by an increase in the voltage on node 408. At the point3006, the regulated voltage is output to the CPU 457.

Referring now to FIG. 31, there is illustrated a flowchart for theoperation of the headset. The operation is initiated at a block 3102 andthen proceeds to a block 3104 wherein the maximum power is transmitted,i.e., that being the power required to provide the initial voltage onthe node 408. This could be the maximum voltage of the headset or couldbe an intermediate voltage that was predetermined. The program thenflows to a decision block 3106 to determine if the CPU 457 istransmitting information regarding sensed voltages. If not, the programloops back to a block 3104 to provide the initial charging power to thesupercapacitor 532. Once sensed voltages have been received, this is anindication that the CPU 457 is operating and that the headset can varythe voltage to ensure that only the minimum amount of voltage is inducedon the node 408 in order to maintain current regulation. Anything abovethat results both in dissipation of heat in the current regulator 459and also unwanted conductivity in the coils. The program, after thesensed voltages have been received, flows to a block 3108 to measure theinduced voltage and the battery voltage at the minimum. As notedhereinabove, all of the other sensed voltages associated with operationof the system could also be sensed. The program then flows to a decisionblock 3110 to determine if the difference in the voltage is greater thana predetermined threshold voltage. If yes, then the program flows to ablock 3112 in order to reduce the induced voltage and, if not, theprogram flows to a block 3114 to increase the induced voltage. Theprogram then flows to a decision block 3116 in order to wait for thenext transmitted sensed voltages, which are periodically measured andtransmitted by the CPU 457. In general, however, this is a polledsystem. The IPGs, whether there are one or two IPGs, are given addressesand requests sent to a particular IPG for information regarding itssensed voltage. Alternatively, a request can be sent to a particular IPGfor any information it has queued up for transmission. Thus, a requestis sent to an IPG and then a certain period of time is allowed forreceipt of that information. Thus, when the charging operation isinitiated, the maximum power is transmitted along with periodic requestsfor information. Until this information is received, no changes are madeto the power. Once information is received, the voltages are measured,in this operation, in order to determine whether the voltage should beincreased or decreased.

In the overall charging operation, the initial charge is approximately30 mA and the voltage is adjusted to maintain this 30 mA with theminimum level of an induced voltage on node 408. Once the supercapacitor532 is fully charged, is only necessary to maintain a current ofapproximately 3 mA. Since the supercapacitor 532 is provided forbuffering and storing charge, it is only necessary to periodicallyrecharge supercapacitor 532. Thus, once charged, as indicated by thereceive voltage on the node 2902, the headset can make a determinationthat the charge is above the charge necessary to maintain regulationoperation of the linear regulator 2910. As long as the voltage on thesupercapacitor 532 is above that voltage, no additional charge isrequired. Thus, by monitoring this voltage, a certain level can bedetermined, below which the headset will again increase the voltage atthe headset to maintain the induced voltage on the node 408 above thethreshold necessary to drive 30 mA to the supercapacitor 532. In thisoperation, the amount of current driven to the IPG is managed to reduceunnecessary heating in both the IPG and at the inductive interface.

Certain embodiments disclosed herein may be described as including anexternal charging system (or external charge transfer system) forcharging (or transferring charge to) one or more implantable devices.Strictly speaking, in the described embodiments using a transmit coiland a receive coil, energy is stored per cycle as a magnetic field inthe transmit coil, and some of this energy is transferred per cycle bymagnetic induction to the receive coil. In other words, energy istransferred over a certain duration of time from the transmit coil tothe receive coil, and the rate of such energy transfer is power.However, the words “energy” and “power” are frequently used somewhatinterchangeably when describing a magnetic induction circuit, since acircuit that transfers power (i.e., at a certain rate) also transfers acorresponding amount of energy over a duration of time. As such,disabling power transfer also likewise disables energy transfer whendisabled for a certain period of time. Moreover, reducing power transferalso likewise reduces energy transfer over a period of time. For thisreason, in context there is seldom confusion between usage of thephrases “transferred energy” and “transferred power”, or between thephrases “received energy” and “received power,” as it is usually clearin context whether the reference is to total transfer over a duration oftime, or to an instantaneous rate of transfer.

The phrases “power transfer” or “energy transfer” may also be somewhatinformally referred to as “charge transfer” because such transferredcharge may be for delivering power, in the form of a current (i.e.,moving electronic charge) at a certain voltage, to operate circuitrywithin the implantable device, in addition to (or instead of) charging asupercapacitor, battery, or other charge storage device within theimplantable device. Consequently, as used herein, an external chargingsystem may also be viewed as an external charge transfer system or anexternal power transfer system, and references herein to an externalcharging system, an external charge transfer system, and an externalpower transfer system may be used interchangeably with no specificdistinction intended unless clear in the context of such use, even if nocharge storage device is “charged” in a given embodiment. Similarly, acharge receiving system may also be viewed as a power receiving system,and references herein to a charge receiving system and a power receivingsystem may be used interchangeably with no specific distinction intendedunless clear in the context of such use.

It is to be understood that the implementations disclosed herein are notlimited to the particular systems or processes described which might, ofcourse, vary. It is also to be understood that the terminology usedherein is for the purpose of describing particular implementations only,and is not intended to be limiting. As used in this specification, thesingular forms “a”, “an” and “the” include plural referents unless thecontent clearly indicates otherwise.

As used herein, “exemplary” is used interchangeably with “an example.”For instance, an exemplary embodiment means an example embodiment, andsuch an example embodiment does not necessarily include essentialfeatures and is not necessarily preferred over another embodiment. Asused herein, “coupling” includes direct and/or indirect coupling ofcircuit components, structural members, etc. As used herein, a group ofone or more transmit coils disposed in series can mean only one transmitcoil, or can mean two or more transmit coils disposed in series.

Regarding terminology used herein, it will be appreciated by one skilledin the art that any of several expressions may be equally well used whendescribing the operation of a circuit including the various signals andnodes within the circuit. Any kind of signal, whether a logic signal ora more general analog signal, takes the physical form of a voltage level(or for some circuit technologies, a current level) of a node within thecircuit. Such shorthand phrases for describing circuit operation usedherein are more efficient to communicate details of circuit operation,particularly because the schematic diagrams in the figures clearlyassociate various signal names with the corresponding circuit blocks andnodes.

Although the present disclosure has been described in detail, it shouldbe understood that various changes, substitutions and alterations may bemade herein without departing from the spirit and scope of thedisclosure as defined by the appended claims. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure,processes, machines, manufacture, compositions of matter, means,methods, or steps, presently existing or later to be developed thatperform substantially the same function or achieve substantially thesame result as the corresponding embodiments described herein may beutilized according to the present disclosure. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

It will be appreciated by those skilled in the art having the benefit ofthis disclosure that this implantable neurostimulation system for headpain provides an implantable neurostimulation system having a pluralityof electrode arrays spaced along a portion of its length such that whenneurostimulation lead is implanted, at least one electrode array ispositioned over the frontal region, at least one electrode array ispositioned over the parietal region, and at least one electrode array ispositioned over the occipital region of the patient's cranium so thatwhen the neurostimulation lead is connected to an implantable pulsegenerator, the single lead can provide medically acceptableneurostimulation coverage over the supraorbital, the auriculotemporal,and the occipital nerves unilaterally. It should be understood that thedrawings and detailed description herein are to be regarded in anillustrative rather than a restrictive manner, and are not intended tobe limiting to the particular forms and examples disclosed. On thecontrary, included are any further modifications, changes,rearrangements, substitutions, alternatives, design choices, andembodiments apparent to those of ordinary skill in the art, withoutdeparting from the spirit and scope hereof, as defined by the followingclaims. Thus, it is intended that the following claims be interpreted toembrace all such further modifications, changes, rearrangements,substitutions, alternatives, design choices, and embodiments.

What is claimed is:
 1. A system for driving an implantableneurostimulator lead having a plurality of electrodes disposed in atleast one array, comprising: an implantable pulse generator (IPG),including: an electrode driver for driving the electrodes, a currentlimiting current regulator for limiting the current to the IPG, a loadsystem for determining a minimum load requirement of the IPG to providethe necessary power to the current regulator, an IPG power coupler forreceiving power across a dermis layer for interface of the power withthe electrode driver, and an IPG communication system for transmittingthe determined minimum load requirement of the IPG across the dermislayer; and an external unit including: an external variable powergenerator, an external power coupler for coupling power across thedermis layer to the IPG power coupler, an external communication systemfor receiving from the IPG communication system the determined minimumload requirement of the IPG, and a controller for varying the powerlevel of the variable power generator as a function of the receiveddetermined minimum load requirement of the IPG.
 2. The system of claim1, wherein the load system comprises: a detector for detecting the stateof the current regulator; and a processor for determining the necessarypower from the external unit required by the electrode driver as thedetermined minimum load requirement of the IPG to maintain the currentregulator in regulation.
 3. The system of claim 2, wherein the currentregulator delivers a predetermined constant current.
 4. The system ofclaim 3, wherein the determined minimum load requirement comprises atleast enough power from the external unit to provide the predeterminedconstant current from the current regulator.
 5. The system of claim 1,wherein the IPG further includes a charge storage device.
 6. The systemof claim 1, wherein the IPG is head-located beneath the dermis layer ofa patient.
 7. The system of claim 1, wherein the IPG communicationsystem and the external communication system each comprises at least onecoil.
 8. A system for driving a plurality of implantable neurostimulatorleads, each lead having an associated plurality of electrodes disposedin at least one array on the lead, the system comprising: at least twoimplantable pulse generators (IPGs), each IPG including: an electrodedriver for driving the electrodes associated with the IPG, a currentlimiting current regulator for limiting the current to the IPG, a loadsystem for determining a minimum load requirement of the IPG to providethe necessary power to the current regulator, an IPG power coupler forreceiving power across a dermis layer for interface of the power withthe electrode driver of the IPG, and an IPG communication system fortransmitting the determined minimum load requirement of the IPG acrossthe dermis layer; and an external unit for providing power to the atleast two IPGs, the external unit including: an external variable powergenerator, an external power coupler for coupling power across thedermis layer to the IPG power couplers, an external communication systemfor receiving from the IPG communication systems the respectivedetermined minimum load requirements, and a controller for varying thepower level of the variable power generator as a function of thereceived determined minimum load requirement of the IPG with thegreatest minimum load requirement.
 9. The system of claim 8, wherein thecommunication systems of each IPG is operable to transmit the determinedminimum load requirement to the external communication systemindependently of the communication systems of each of the other IPGs.10. The system of claim 8, wherein each of the IPG communication systemstransmits its respective determined minimum load requirement to theexternal unit communication system inductively.
 11. The system of claim8, wherein each IPG power coupler is for receiving levels of poweracross a dermis layer that are independent of the levels of powerreceived by the power couplers of each of the other IPGs.
 12. The systemof claim 8, wherein at least one of the IPGs further includes a chargestorage device.